_437.java

package com.fishercoder.solutions.firstthousand;

import com.fishercoder.common.classes.TreeNode;

public class _437 {

    public static class Solution1 {
        public int pathSum(TreeNode root, int sum) {
            if (root == null) {
                return 0;
            }
            return pathSumFrom(root, sum) + pathSum(root.left, sum) + pathSum(root.right, sum);
        }

        private int pathSumFrom(TreeNode root, int sum) {
            if (root == null) {
                return 0;
            }
            return (root.val == sum ? 1 : 0)
                    + pathSumFrom(root.left, sum - root.val)
                    + pathSumFrom(root.right, sum - root.val);
        }
    }
}