LC112-Path-Sum.java

/*
Given the root of a binary tree and an integer targetSum, return true if
the tree has a root-to-leaf path such that adding up all the values along
the path equals targetSum.

A leaf is a node with no children.

Example 1:
Input: root = [5,4,8,11,null,13,4,7,2,null,null,null,1], targetSum = 22
Output: true

Example 2:
Input: root = [1,2,3], targetSum = 5
Output: false

Example 3:
Input: root = [1,2], targetSum = 0
Output: false


Constraints:
The number of nodes in the tree is in the range [0, 5000].
-1000 <= Node.val <= 1000
-1000 <= targetSum <= 1000
*/

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
class Solution {
    public boolean hasPathSum(TreeNode root, int targetSum) {
        if (root == null){
            return false;
        }
        // if the root node is a leaf -> straight-forward
        if ((root.left == null) && (root.right == null)){
            return root.val == targetSum;
        }
        // check if leftTree has a path sum targetSum - root.val
        if ((root.left != null) && (hasPathSum(root.left, targetSum-root.val)))
            return true;
        // do same for the right tree
        if ((root.right != null) && (hasPathSum(root.right, targetSum-root.val)))
            return true;

        return false;
    }
}