# LeetCode - 437. Path sum III

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遍历整棵树，每个节点找一遍
/**
* Definition for a binary tree node.
* public class TreeNode {
*     int val;
*     TreeNode left;
*     TreeNode right;
*     TreeNode(int x) { val = x; }
* }
*/
class Solution {
int cnt = 0;
public int pathSum(TreeNode root, int sum) {
if (root == null)
return 0;
find(root, sum);
pathSum(root.left, sum);
pathSum(root.right, sum);
return cnt;
}

private void find(TreeNode node, int sum) {
if (node == null)
return;
if (sum == node.val)
cnt ++;
find(node.left, sum-node.val);
find(node.right, sum-node.val);
}
}

posted @ 2018-10-15 17:14  Pickle  阅读(150)  评论(0编辑  收藏  举报