[leetcode]Path Sum

简单题。递归。

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