LeetCode 677. 键值映射

一个简单的Tire树模板题，存个档

class MapSum {

struct TrieNode {
    TrieNode* next[26];
    int val;
    TrieNode() {
        for(int i = 0; i < 26; i++) 
            this->next[i] = NULL;
        this->val = 0;
    }
};

public:
    MapSum() {
        root = new TrieNode();
    }
    
    void insert(string key, int val) {
        int delta = val;
        if(cnt.count(key))
            delta -= cnt[key];
        cnt[key] = val;
        TrieNode* node = root;
        for(auto c : key) {
            if(node->next[c - 'a'] == NULL)
                node->next[c - 'a'] = new TrieNode();
            node = node->next[c - 'a'];
            node->val += delta;
        }
    }
    
    int sum(string prefix) {
        TrieNode* node = root;
        for(auto c : prefix) {
            if(node->next[c - 'a'] == NULL)
                return 0;
            node = node->next[c-'a'];
        }
        return node->val;
    }
private:
    unordered_map<string, int> cnt;
    TrieNode* root;
};