My code:

/**
 * 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;
        return hasPathSum(root, 0, sum);
    }
    
    private boolean hasPathSum(TreeNode root, int sum, int totalSum) {
        if (root == null)
            return false;
        if (root.left == null && root.right == null) {
            if (sum + root.val == totalSum)
                return true;
            else
                return false;
        }
        else
            return hasPathSum(root.left, sum + root.val, totalSum) | hasPathSum(root.right, sum + root.val, totalSum);
            
    }
}

My test result:

我的算法不是很好，但是勉强凑活吧。
就是一个DFS。

**
总结： Tree DFS
**

Anyway, Good luck, Richardo!

My code:

/**
 * 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;
        }
        
        return helper(root, 0, sum);
    }
    
    private boolean helper(TreeNode root, int curr, int sum) {
        if (root.left == null && root.right == null) {
            if (curr + root.val == sum) {
                return true;
            }
            else {
                return false;
            }
        }
        else {
            if (root.left != null) {
                boolean flag = helper(root.left, curr + root.val, sum);
                if (flag) {
                    return true;
                }
            }
            if (root.right != null) {
                boolean flag = helper(root.right, curr + root.val, sum);
                if (flag) {
                    return true;
                }
            }
            return false;
        }
    }
}

简单题，没什么好说的。

Anyway, Good luck, Richardo! -- 08/28/2016