PathSum.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.

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*/

/**
 * Definition for binary tree
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */

public class PathSum {
    public boolean hasPathSum(TreeNode root, int sum) {
       if (root == null) return false;
       if (root.left == null && root.right == null) return sum == root.val;
       return hasPathSum(root.left, sum - root.val) || hasPathSum(root.right, sum - root.val);
    }
}