leetcode_question_112 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.

DFS:

bool findPathSum(TreeNode* root, vector<int> &path, int sum)
    {
    	path.push_back(root->val);
		if(root->left == NULL && root->right == NULL){
			vector<int>::iterator it = path.begin();
			int tmpsum = 0;
			for(; it != path.end(); ++it)
				tmpsum += *it;
			path.pop_back();
			if(tmpsum == sum)
				return true;
			else 
				return false;
		}
		bool flag = false;
		if(root->left)
			flag = findPathSum(root->left,path,sum);
		if(!flag && root->right)
			flag = findPathSum(root->right,path,sum);
		path.pop_back();
		return flag;
	}
	bool hasPathSum(TreeNode *root, int sum) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        if(root == NULL)
			return false;
		vector<int> path;
		return findPathSum(root, path,sum);
    }