[LeetCode] Path Sum

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.

[Solution].java

/**
 * 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) {
        // Start typing your Java solution below
        // DO NOT write main() function
        return hasPathSum(0, root, sum);
    }

    private boolean hasPathSum(int last, TreeNode root, int sum){
        if(root == null) return false;
        int now = last + root.val;

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