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,

  1.               5
  2.              / \
  3.             4   8
  4.            /   / \
  5.           11  13  4
  6.          /  \      \
  7.         7    2      1

return true, as there exist a root-to-leaf path 5->4->11->2 which sum is 22.

Solution:

  1. /**
  2.  * Definition for a binary tree node.
  3.  * public class TreeNode {
  4.  *     int val;
  5.  *     TreeNode left;
  6.  *     TreeNode right;
  7.  *     TreeNode(int x) { val = x; }
  8.  * }
  9.  */
  10. public class Solution {
  11.   public boolean hasPathSum(TreeNode root, int sum) {
  12.     if (root == null)
  13.       return false;
  15.     if (root.left == null && root.right == null && root.val == sum)
  16.       return true;
  18.     return hasPathSum(root.left, sum - root.val) || hasPathSum(root.right, sum - root.val);
  19.   }
  20. }