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Polish compress solution.

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Donne Martin 2016-02-09 06:49:29 -05:00
parent 81f0f0c1af
commit 9bf96eabaa
1 changed files with 27 additions and 49 deletions
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76
arrays_strings/compress/compress_solution.ipynb
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@ -60,26 +60,24 @@
"source": [
"## Algorithm\n",
"\n",
"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",
"\n",
"* Calculate the size of the compressed string\n",
" * Note the constraint about compressing only if it saves space\n",
"* If the compressed string size is >= string size, return string\n",
"* Create compressed_string\n",
" * For each char in string\n",
" * If char is the same as last_char, increment count\n",
" * Else\n",
" * Append last_char to compressed_string\n",
" * append count to compressed_string\n",
" * count = 1\n",
" * last_char = char\n",
" * Append last_char to compressed_string\n",
" * Append count to compressed_string\n",
" * Return compressed_string\n",
"* For each char in string\n",
" * If char is the same as last_char, increment count\n",
" * Else\n",
" * Append last_char and count to compressed_string\n",
" * last_char = char\n",
" * count = 1\n",
"* Append last_char and count to compressed_string\n",
"* If the compressed string size is < string size\n",
" * Return compressed string\n",
"* Else\n",
" * Return string\n",
"\n",
"Complexity:\n",
"* Time: O(n)\n",
"* Space: O(n)"
"* Space: O(n)\n",
"\n",
"Complexity Note:\n",
"* Although strings are immutable in Python, appending to strings is optimized in CPython so that it now runs in O(n) and extends the string in-place. Refer to this [Stack Overflow post](http://stackoverflow.com/a/4435752)."
]
},
{
@ -100,38 +98,18 @@
"def compress_string(string):\n",
" if string is None or len(string) == 0:\n",
" return string\n",
"\n",
" # Calculate the size of the compressed string\n",
" size = 0\n",
" last_char = string[0]\n",
" for char in string:\n",
" if char != last_char:\n",
" size += 2\n",
" last_char = char\n",
" size += 2\n",
"\n",
" # If the compressed string size is greater than\n",
" # or equal to string size, return original string\n",
" if size >= len(string):\n",
" return string\n",
"\n",
" # Create compressed_string\n",
" compressed_string = list()\n",
" result = ''\n",
" prev_char = string[0]\n",
" count = 0\n",
" last_char = string[0]\n",
" for char in string:\n",
" if char == last_char:\n",
" if char == prev_char:\n",
" count += 1\n",
" else:\n",
" compressed_string.append(last_char)\n",
" compressed_string.append(str(count))\n",
" result += prev_char + str(count)\n",
" prev_char = char\n",
" count = 1\n",
" last_char = char\n",
" compressed_string.append(last_char)\n",
" compressed_string.append(str(count))\n",
"\n",
" # Convert the characters in the list to a string\n",
" return \"\".join(compressed_string)"
" result += prev_char + str(count)\n",
" return result if len(result) < len(string) else string"
]
},
{
@ -202,21 +180,21 @@
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