mirror of
https://github.com/donnemartin/interactive-coding-challenges.git
synced 2024-03-22 13:11:13 +08:00
317 lines
9.1 KiB
Python
317 lines
9.1 KiB
Python
{
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"cells": [
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"This notebook was prepared by [hashhar](https://github.com/hashhar), second solution added by [janhak](https://github.com/janhak). Source and license info is on [GitHub](https://github.com/donnemartin/interactive-coding-challenges)."
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"# Solution Notebook"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"## Problem: Compress a string such that 'AAABCCDDDD' becomes 'A3BCCD4'. Only compress the string if it saves space.\n",
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"\n",
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"* [Constraints](#Constraints)\n",
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"* [Test Cases](#Test-Cases)\n",
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"* [Algorithm](#Algorithm)\n",
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"* [Code](#Code)\n",
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"* [Unit Test](#Unit-Test)"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"## Constraints\n",
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"\n",
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"* Can we assume the string is ASCII?\n",
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" * Yes\n",
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" * Note: Unicode strings could require special handling depending on your language\n",
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"* Is this case sensitive?\n",
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" * Yes\n",
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"* Can we use additional data structures? \n",
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" * Yes\n",
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"* Can we assume this fits in memory?\n",
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" * Yes"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"## Test Cases\n",
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"\n",
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"* None -> None\n",
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"* '' -> ''\n",
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"* 'AABBCC' -> 'AABBCC'\n",
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"* 'AAABCCDDDD' -> 'A3BCCD4'"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"## Algorithm\n",
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"\n",
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"Since Python strings are immutable, we'll use a list of characters to build the compressed string representation. We'll then convert the list to a string.\n",
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"\n",
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"* Calculate the size of the compressed string\n",
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" * Note the constraint about compressing only if it saves space\n",
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"* If the compressed string size is >= string size, return string\n",
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"* Create compressed_string\n",
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" * For each char in string\n",
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" * If char is the same as last_char, increment count\n",
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" * Else\n",
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" * If the count is more than 2\n",
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" * Append last_char to compressed_string\n",
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" * append count to compressed_string\n",
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" * count = 1\n",
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" * last_char = char\n",
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" * If count is 1\n",
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" * Append last_char to compressed_string\n",
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" * count = 1\n",
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" * last_char = char\n",
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" * If count is 2\n",
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" * Append last_char to compressed_string\n",
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" * Append last_char to compressed_string once more\n",
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" * count = 1\n",
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" * last_char = char\n",
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" * Append last_char to compressed_string\n",
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" * Append count to compressed_string\n",
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" * Return compressed_string\n",
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"\n",
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"Complexity:\n",
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"* Time: O(n)\n",
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"* Space: O(n)"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"## Code"
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]
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},
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{
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"cell_type": "code",
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"execution_count": 1,
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"metadata": {},
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"outputs": [],
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"source": [
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"def compress_string(string):\n",
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" if string is None or len(string) == 0:\n",
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" return string\n",
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"\n",
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" # Calculate the size of the compressed string\n",
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" size = 0\n",
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" last_char = string[0]\n",
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" for char in string:\n",
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" if char != last_char:\n",
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" size += 2\n",
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" last_char = char\n",
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" size += 2\n",
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"\n",
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" # If the compressed string size is greater than\n",
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" # or equal to string size, return original string\n",
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" if size >= len(string):\n",
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" return string\n",
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"\n",
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" # Create compressed_string\n",
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" # New objective:\n",
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" # Single characters are to be left as is\n",
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" # Double characters are to be left as are\n",
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" compressed_string = list()\n",
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" count = 0\n",
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" last_char = string[0]\n",
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" for char in string:\n",
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" if char == last_char:\n",
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" count += 1\n",
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" else:\n",
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" # Do the old compression tricks only if count exceeds two\n",
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" if count > 2:\n",
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" compressed_string.append(last_char)\n",
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" compressed_string.append(str(count))\n",
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" count = 1\n",
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" last_char = char\n",
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" # If count is either 1 or 2\n",
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" else:\n",
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" # If count is 1, leave the char as is\n",
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" if count == 1:\n",
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" compressed_string.append(last_char)\n",
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" count = 1\n",
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" last_char = char\n",
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" # If count is 2, append the character twice\n",
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" else:\n",
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" compressed_string.append(last_char)\n",
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" compressed_string.append(last_char)\n",
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" count = 1\n",
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" last_char = char\n",
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" compressed_string.append(last_char)\n",
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" compressed_string.append(str(count))\n",
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"\n",
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" # Convert the characters in the list to a string\n",
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" return \"\".join(compressed_string)"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"## Algorithm: Split to blocks and compress\n",
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"\n",
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"Let us split the string first into blocks of identical characters and then compress it block by block.\n",
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"\n",
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"* Split the string to blocks\n",
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" * For each character in string\n",
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" * Add this character to block\n",
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" * If the next character is different\n",
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" * Return block\n",
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" * Erase the content of block\n",
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"\n",
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"\n",
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"* Compress block\n",
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" * If block consists of two or fewer characters\n",
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" * Return block\n",
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" * Else\n",
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" * Append length of the block to the first character and return\n",
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"\n",
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"\n",
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"* Compress string\n",
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" * Split the string to blocks\n",
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" * Compress blocks\n",
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" * Join compressed blocks\n",
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" * Return result if it is shorter than original string\n",
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"\n",
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"Complexity:\n",
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"* Time: O(n)\n",
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"* Space: O(n)"
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]
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},
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{
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"cell_type": "code",
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"execution_count": 2,
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"metadata": {},
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"outputs": [],
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"source": [
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"def split_to_blocks(string):\n",
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" block = ''\n",
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" for char, next_char in zip(string, string[1:] + ' '):\n",
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" block += char\n",
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" if char is not next_char:\n",
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" yield block\n",
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" block = ''\n",
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"\n",
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"\n",
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"def compress_block(block):\n",
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" if len(block) <= 2:\n",
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" return block\n",
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" else:\n",
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" return block[0] + str(len(block))\n",
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"\n",
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"\n",
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"def compress_string(string):\n",
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" if string is None or not string:\n",
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" return string\n",
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" compressed = (compress_block(block) for block in split_to_blocks(string))\n",
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" result = ''.join(compressed)\n",
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" return result if len(result) < len(string) else string"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"## Unit Test"
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]
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},
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{
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"cell_type": "code",
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"execution_count": 3,
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"metadata": {},
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"outputs": [
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{
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"name": "stdout",
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"output_type": "stream",
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"text": [
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"Overwriting test_compress.py\n"
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]
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}
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],
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"source": [
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"%%writefile test_compress.py\n",
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"import unittest\n",
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"\n",
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"\n",
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"class TestCompress(unittest.TestCase):\n",
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"\n",
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" def test_compress(self, func):\n",
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" self.assertEqual(func(None), None)\n",
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" self.assertEqual(func(''), '')\n",
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" self.assertEqual(func('AABBCC'), 'AABBCC')\n",
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" self.assertEqual(func('AAABCCDDDD'), 'A3BCCD4')\n",
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" self.assertEqual(\n",
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" func('aaBCCEFFFFKKMMMMMMP taaammanlaarrrr seeeeeeeeek tooo'),\n",
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" 'aaBCCEF4KKM6P ta3mmanlaar4 se9k to3',\n",
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" )\n",
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" print('Success: test_compress')\n",
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"\n",
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"\n",
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"def main():\n",
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" test = TestCompress()\n",
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" test.test_compress(compress_string)\n",
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"\n",
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"\n",
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"if __name__ == '__main__':\n",
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" main()"
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]
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},
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{
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"cell_type": "code",
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"execution_count": 4,
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"metadata": {},
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"outputs": [
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{
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"name": "stdout",
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"output_type": "stream",
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"text": [
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"Success: test_compress\n"
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]
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}
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],
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"source": [
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"%run -i test_compress.py"
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]
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}
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],
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"metadata": {
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"kernelspec": {
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"display_name": "Python 3",
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"language": "python",
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"name": "python3"
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},
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"language_info": {
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"codemirror_mode": {
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"name": "ipython",
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"version": 3
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},
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"file_extension": ".py",
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"mimetype": "text/x-python",
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"name": "python",
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"nbconvert_exporter": "python",
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"pygments_lexer": "ipython3",
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"version": "3.7.2"
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}
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},
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"nbformat": 4,
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"nbformat_minor": 1
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}
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