112_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.
 */
/**
 * Definition for binary tree
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */

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