LeetCode 677. 键值映射

思路

字典树，边插入边更新sum

代码实现

class MapSum {
    class Trie {
        public:
            bool isWord = false;
            int value = 0;
            int sum = 0;
            Trie* next[26] = {NULL};

            //判断word是否已经存在，返回其对应的value
            int isExist(const string word) {
                Trie* t = this;
                for(int i = 0; i < word.length(); ++i){
                    if(t->next[word[i]-'a'] == NULL) 
                        return 0;
                    
                    t = t->next[word[i]-'a'];
                }

                if(t->isWord == true)
                    return t->value;
                return 0;
            }

            void insert(const string word, int val) {
                update(word, isExist(word), val);
            }

            void update(const string word, int oldVal, int newVal) {
                Trie* t = this;
                for(int i = 0; i < word.length(); ++i){
                    if(t->next[word[i]-'a'] == NULL) {
                        t->next[word[i]-'a'] = new Trie();
                    }

                    t = t->next[word[i]-'a'];
                    t->sum = t->sum - oldVal + newVal;  
                }

                t->isWord = true;
                t->value = newVal;
            }

            int getSum(const string word) {
                Trie* t = this;
                for(int i = 0; i < word.length(); ++i){
                    if(t->next[word[i]-'a'] == NULL) {
                        return 0;
                    }

                    t = t->next[word[i]-'a'];
                }

                return t->sum;
            }


    };
    
public:
    /** Initialize your data structure here. */
    MapSum() {

    }

    Trie* t = new Trie();
    
    void insert(string key, int val) {
        t->insert(key, val);
    }
    
    int sum(string prefix) {
        return t->getSum(prefix);
    }
};

/**
 * Your MapSum object will be instantiated and called as such:
 * MapSum* obj = new MapSum();
 * obj->insert(key,val);
 * int param_2 = obj->sum(prefix);
 */