面试题34-I 二叉树中和为某一值的路径是否存在

题目：

 

 

解答：

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    bool hasPathSum(TreeNode* root, int sum) 
    {
        return helper(root, 0, sum);        
    }

    bool helper(TreeNode * root, int cur, int sum)
    {
        if (NULL == root)
        {
            return false;
        }

        cur = cur + root->val;
        
        if (root->left == NULL && root->right == NULL)
        {
            return cur == sum;
        }
        else
        {
            return helper(root->left, cur, sum) || helper(root->right, cur, sum);
        }
    }
};