LeetCode 677. 键值映射
思路
字典树，边插入边更新sum
代码实现
1 class MapSum { 2 class Trie { 3 public: 4 bool isWord = false; 5 int value = 0; 6 int sum = 0; 7 Trie* next[26] = {NULL}; 8 9 //判断word是否已经存在，返回其对应的value 10 int isExist(const string word) { 11 Trie* t = this; 12 for(int i = 0; i < word.length(); ++i){ 13 if(t->next[word[i]-'a'] == NULL) 14 return 0; 15 16 t = t->next[word[i]-'a']; 17 } 18 19 if(t->isWord == true) 20 return t->value; 21 return 0; 22 } 23 24 void insert(const string word, int val) { 25 update(word, isExist(word), val); 26 } 27 28 void update(const string word, int oldVal, int newVal) { 29 Trie* t = this; 30 for(int i = 0; i < word.length(); ++i){ 31 if(t->next[word[i]-'a'] == NULL) { 32 t->next[word[i]-'a'] = new Trie(); 33 } 34 35 t = t->next[word[i]-'a']; 36 t->sum = t->sum - oldVal + newVal; 37 } 38 39 t->isWord = true; 40 t->value = newVal; 41 } 42 43 int getSum(const string word) { 44 Trie* t = this; 45 for(int i = 0; i < word.length(); ++i){ 46 if(t->next[word[i]-'a'] == NULL) { 47 return 0; 48 } 49 50 t = t->next[word[i]-'a']; 51 } 52 53 return t->sum; 54 } 55 56 57 }; 58 59 public: 60 /** Initialize your data structure here. */ 61 MapSum() { 62 63 } 64 65 Trie* t = new Trie(); 66 67 void insert(string key, int val) { 68 t->insert(key, val); 69 } 70 71 int sum(string prefix) { 72 return t->getSum(prefix); 73 } 74 }; 75 76 /** 77 * Your MapSum object will be instantiated and called as such: 78 * MapSum* obj = new MapSum(); 79 * obj->insert(key,val); 80 * int param_2 = obj->sum(prefix); 81 */
