You are given a binary tree in which each node contains an integer value.
Find the number of paths that sum to a given value.
The path does not need to start or end at the root or a leaf, but it must go downwards (traveling only from parent nodes to child nodes).
The tree has no more than 1,000 nodes and the values are in the range -1,000,000 to 1,000,000.
Example:
root = [10,5,-3,3,2,null,11,3,-2,null,1], sum = 8
10
/ 5 -3
/ \ 3 2 11
/ \ 3 -2 1
Return 3. The paths that sum to 8 are:
1. 5 -> 3
2. 5 -> 2 -> 1
3. -3 -> 11
1 class Solution { 2 3 public int pathSum(TreeNode root, int sum) { 4 if(root==null) return 0; 5 int res = path(root,sum)+pathSum(root.right,sum)+pathSum(root.left,sum); 6 return res; 7 8 } 9 10 private int path(TreeNode root, int sum) { 11 int res=0; 12 if(root==null) 13 return res ; 14 if(sum==root.val) 15 res+=1; 16 res+=path(root.left,sum-root.val); 17 res+=path(root.right,sum-root.val); 18 return res; 19 } 20 21 }
原文：http://www.cnblogs.com/zle1992/p/7842810.html