力扣677.键值映射

• 字典树

  • 求值时，先把node移动到前缀的末尾
  • 再从末尾开始匹配

•   class MapSum {
    private:
        int val;
        MapSum* next[26];
    public:
        MapSum() {
            val = 0;
            memset(next,0,sizeof(next));
        }
        
        void insert(string key, int val) {
            MapSum* node = this;
            for(char c:key)
            {
                if(node->next[c-'a'] == NULL)
                    node->next[c-'a'] = new MapSum();
                node = node->next[c-'a'];
            }
            node->val = val;
        }
        
        int sum(string prefix) {
            MapSum* node = this;
            for(char c:prefix)
            {
                if(node->next[c-'a'] == NULL)
                    return 0;
                node = node->next[c-'a'];
            }
            int sum = 0;
            match(node,sum);
            return sum;
        }
    
        void match(MapSum* node,int& sum)
        {
            //先加当前节点的值
            sum += node->val;
            for(auto& next : node->next)
                //如果next存在 递归
                if(next)
                    match(next,sum);
        }
    };