Path Sum

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.

For 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.

Solution

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
      public boolean hasPathSum(TreeNode root, int sum) {
        return hasPathSum(root, sum, 0);
    }

    public boolean hasPathSum(TreeNode root, int sum, int current) {
        if (root == null) return false;

        if (root.left == null && root.right == null) {
            if (current + root.val == sum) {
                return true;
            } else {
                return false;
            }
        } else if (root.left == null) {
            return hasPathSum(root.right, sum, current + root.val);
        } else if (root.right == null) {
            return hasPathSum(root.left, sum, current + root.val);
        } else {
            return hasPathSum(root.right, sum, current + root.val)||hasPathSum(root.left, sum, current + root.val);
        }
    }
}