LeetCode677. 键值映射（Trie树）

1. 题目

实现一个 MapSum 类里的两个方法，insert 和 sum。

对于方法 insert，你将得到一对（字符串，整数）的键值对。字符串表示键，整数表示值。如果键已经存在，那么原来的键值对将被替代成新的键值对。

对于方法 sum，你将得到一个表示前缀的字符串，你需要返回所有以该前缀开头的键的值的总和。

输入: insert("apple", 3), 输出: Null
输入: sum("ap"), 输出: 3
输入: insert("app", 2), 输出: Null
输入: sum("ap"), 输出: 5

2. Trie树解题

参考：Trie树

class TrieNode
{
public:TrieNode *next[26];int count;TrieNode():count(0){memset(next,NULL,26*sizeof(TrieNode*));}~TrieNode(){}
};class MapSum {TrieNode *root;
public:/** Initialize your data structure here. */MapSum() {root = new TrieNode();}void insert(string key, int val) {TrieNode *cur = root;for(char ch:key){if(cur->next[ch-'a'] == NULL)cur->next[ch-'a'] = new TrieNode();cur = cur->next[ch-'a'];}cur->count = val;}int sum(string prefix) {TrieNode *cur = root;for(char ch:prefix){if(cur->next[ch-'a'] == NULL)return 0;elsecur = cur->next[ch-'a'];}int sumVal = 0;sumVal += cur->count;for(int i = 0; i < 26; ++i)if(cur->next[i])sumVal += sum(cur->next[i]);return sumVal;}
private:int sum(TrieNode *root)//递归求和{int subsum = 0;if(root == NULL)return 0;subsum += root->count;for(int i = 0; i < 26; ++i)if(root->next[i])subsum += sum(root->next[i]);return subsum;}    	
};

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class trie{ // 2021.8.28
public:int v = 0;trie* next[26] = {NULL};void insert(string& s, int val){trie* cur = this;for(auto ch : s){if(!cur->next[ch-'a'])cur->next[ch-'a'] = new trie();cur = cur->next[ch-'a'];}cur->v = val;}void find(trie* root, string& s, int i, int &sum){if(!root) return;if(i<s.size()&&root->next[s[i]-'a'])find(root->next[s[i]-'a'], s, i+1, sum);else if(i==s.size()){sum += root->v;for(int j = 0; j < 26; ++j){if(root->next[j]){find(root->next[j], s, i, sum);}}}}
};
class MapSum {trie* root;
public:/** Initialize your data structure here. */MapSum() {root = new trie();}void insert(string key, int val) {root->insert(key,val);}int sum(string prefix) {int tot = 0;root->find(root, prefix, 0, tot);return tot;}
};/*** Your MapSum object will be instantiated and called as such:* MapSum* obj = new MapSum();* obj->insert(key,val);* int param_2 = obj->sum(prefix);*/