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 */
