No112.path-sum.cs

/*
 * Difficulty:
 * Medium
 *
 * Desc:
 * Given a binary tree and a sum, determine if the tree has a root-to-leaf path such that adding up all the values along the path equals the given sum.
 * Note: A leaf is a node with no children.
 *
 * Example:
 * Given the below binary tree and sum = 22,
 *      5
 *     / \
 *    4   8
 *   /   / \
 *  11  13  4
 * /  \      \
 * 7    2      1
 * return true, as there exist a root-to-leaf path 5->4->11->2 which sum is 22.
*/

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     public int val;
 *     public TreeNode left;
 *     public TreeNode right;
 *     public TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    private bool PathSum(TreeNode node, int sum, int target) {
        if (node.left == null && node.right == null) return sum + node.val == target;
        return (node.left != null && PathSum(node.left, sum + node.val, target)) || (node.right != null && PathSum(node.right, sum + node.val, target));
    }

    public bool HasPathSum(TreeNode root, int sum) {
        if (root == null) return false;
        return PathSum(root, 0, sum);
    }
}