437. Path Sum III

 1 /**
 2  * Definition for a binary tree node.
 3  * struct TreeNode {
 4  *     int val;
 5  *     TreeNode *left;
 6  *     TreeNode *right;
 7  *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 8  * };
 9  */
10 class Solution 
11 {
12 public:
13     int helper(TreeNode* root,unordered_map<int,int> &map,int sum,int target)
14     {
15         if(root==NULL)
16             return 0;
17         sum+=root->val;
18         int res=0;
19         if(map.count(sum-target))
20             res=map[sum-target];
21         map[sum]++;
22         res+=helper(root->left,map,sum,target);
23         res+=helper(root->right,map,sum,target);
24         map[sum]--;
25         return res;        
26     }
27       
28     int pathSum(TreeNode* root, int sum) 
29     {
30         unordered_map<int,int> map;
31         map[0]=1;
32         return helper(root,map,0,sum);
33     }
34 };