leeetcode 112.Path Sum

　　递归实现：

　　

/**
 * Definition for a binary tree node.
 * 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;
        }
        
        else if(root.left == null && root.right == null && root.val == sum){
            return true;
        }
        
        else{
            return (hasPathSum(root.left,sum-root.val)||hasPathSum(root.right,sum-root.val));
        }
    }
}