112_Path_Sum.java

/*
  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.
*/

class TreeNode {
    int val;
    TreeNode left;
    TreeNode right;

    TreeNode(int x) {
        val = x;
    }
}

class Solution {

    public boolean hasPathSum(TreeNode root, int sum) {

        if (root == null) {
            return false;
        }

        if (root.left == null && root.right == null) {
            return root.val == sum;
        }

        return hasPathSum(root.left, sum - root.val)
                || hasPathSum(root.right, sum - root.val);
    }
}