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CyC2018 2018-04-22 22:03:33 +08:00
parent f91559d3b5
commit 343a5fa6b8
1 changed files with 45 additions and 36 deletions
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notes/Leetcode 题解.md
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@ -5534,6 +5534,11 @@ Trie，又称前缀树或字典树，用于判断字符串是否存在或者是
```java ```java
class Trie { class Trie {
private class Node {
Node[] childs = new Node[26];
boolean isLeaf;
}
private Node root = new Node(); private Node root = new Node();
public Trie() { public Trie() {
@ -5543,41 +5548,43 @@ class Trie {
insert(word, root); insert(word, root);
} }
private void insert(String word, Node node){ private void insert(String word, Node node) {
int idx = word.charAt(0) - 'a'; if (node == null) return;
if(node.child[idx] == null){ if (word.length() == 0) {
node.child[idx] = new Node(); node.isLeaf = true;
return;
} }
if(word.length() == 1) node.child[idx].isLeaf = true; int index = indexForChar(word.charAt(0));
else insert(word.substring(1), node.child[idx]); if (node.childs[index] == null) {
node.childs[index] = new Node();
}
insert(word.substring(1), node.childs[index]);
} }
public boolean search(String word) { public boolean search(String word) {
return search(word, root); return search(word, root);
} }
private boolean search(String word, Node node){ private boolean search(String word, Node node) {
if(node == null) return false; if (node == null) return false;
int idx = word.charAt(0) - 'a'; if (word.length() == 0) return node.isLeaf;
if(node.child[idx] == null) return false; int index = indexForChar(word.charAt(0));
if(word.length() == 1) return node.child[idx].isLeaf; return search(word.substring(1), node.childs[index]);
return search(word.substring(1), node.child[idx]);
} }
public boolean startsWith(String prefix) { public boolean startsWith(String prefix) {
return startWith(prefix, root); return startWith(prefix, root);
} }
private boolean startWith(String prefix, Node node){ private boolean startWith(String prefix, Node node) {
if(node == null) return false; if (node == null) return false;
if(prefix.length() == 0) return true; if (prefix.length() == 0) return true;
int idx = prefix.charAt(0) - 'a'; int index = indexForChar(prefix.charAt(0));
return startWith(prefix.substring(1), node.child[idx]); return startWith(prefix.substring(1), node.childs[index]);
} }
private class Node{ private int indexForChar(char c) {
Node[] child = new Node[26]; return c - 'a';
boolean isLeaf;
} }
} }
``` ```
@ -5612,15 +5619,16 @@ class MapSum {
} }
private void insert(String key, Node node, int val) { private void insert(String key, Node node, int val) {
int idx = key.charAt(0) - 'a'; if (node == null) return;
if (node.child[idx] == null) { if (key.length() == 0) {
node.child[idx] = new Node(); node.value = val;
return;
} }
if (key.length() == 1) { int index = indexForChar(key.charAt(0));
node.child[idx].value = val; if (node.child[index] == null) {
} else { node.child[index] = new Node();
insert(key.substring(1), node.child[idx], val);
} }
insert(key.substring(1), node.child[index], val);
} }
public int sum(String prefix) { public int sum(String prefix) {
@ -5628,20 +5636,21 @@ class MapSum {
} }
private int sum(String prefix, Node node) { private int sum(String prefix, Node node) {
if (node == null) { if (node == null) return 0;
return 0; if (prefix.length() != 0) {
int index = indexForChar(prefix.charAt(0));
return sum(prefix.substring(1), node.child[index]);
} }
int sum = node.value; int sum = node.value;
if (prefix.length() == 0) { for (Node child : node.child) {
for (Node next : node.child) { sum += sum(prefix, child);
sum += sum(prefix, next);
}
} else {
int idx = prefix.charAt(0) - 'a';
sum = sum(prefix.substring(1), node.child[idx]);
} }
return sum; return sum;
} }
private int indexForChar(char c) {
return c - 'a';
}
} }
``` ```