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.

Solution 1：//DFS

public class Solution {

    public int pathSum(TreeNode root, int sum) {

        if(root == null)

            return 0;

        return dfs(root, sum) + pathSum(root.left, sum) + pathSum(root.right, sum);

    }

 

    private int dfs(TreeNode root, int sum){

        int res = 0;

        if(root == null)

            return res;

        if(sum == root.val)

            res++;

        res += dfs(root.left, sum - root.val);

        res += dfs(root.right, sum - root.val);

        return res;

    }

}