PathSum.java

package easy._112;

import definition.TreeNode;

/**
 * @author Larry
 *
 * 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.
 *
 * Note: A leaf is a node with no children.
 *
 * 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.
 */

public class PathSum {

    public boolean hasPathSum(TreeNode root, int sum) {

        if (root == null) return false;
        sum -= root.val;
        if (root.left == null && root.right == null){
            if (sum == 0) return true;
            else return false;
        } else return hasPathSum(root.left, sum) || hasPathSum(root.right, sum);

    }

}