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.

简单的归递。

public class Solution {    public int pathSum(TreeNode root, int sum) {        if (root == null) return 0;        int res = 0;        res += dfs(root, sum);        res += pathSum(root.left, sum);        res += pathSum(root.right, sum);        return res;    }        private int dfs(TreeNode node, int remain) {        int tmp = 0;        if (node.left != null)            tmp += dfs(node.left, remain-node.val);        if (node.right != null)            tmp += dfs(node.right, remain-node.val);        if (remain == node.val)            tmp++;        return tmp;    }}