0112-path-sum.java

/**
 * 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 {
    private boolean isLeafNode(TreeNode node) {
        return ((node.left == null) && (node.right == null));
    }

    public boolean hasPathSum(TreeNode root, int targetSum) {
        // Edge case: No nodes
        if(root == null) {
            return false;
        }

        targetSum -= root.val;
        if(isLeafNode(root)) {
            return (targetSum == 0);
        }
        return hasPathSum(root.left, targetSum) || hasPathSum(root.right, targetSum);
    }
}