Path Sum II

Given a binary tree and a sum, find all root-to-leaf paths where each path's sum equals the given sum.

For example:
Given the below binary tree and sum = 22,

              5
             / \
            4   8
           /   / \
          11  13  4
         /  \    / \
        7    2  5   1

return

[
   [5,4,11,2],
   [5,8,4,5]
]
struct Node
{
	int val;
	Node *left;
	Node *right;
	Node(int v)
	{
		val = v;
		left = right = NULL;
	}
};

void visit(Node *root, int target, int sum, vector<int> &a, vector<vector<int> > &result)
{
	if (root == NULL)
	{
		return;
	}
	
	sum += root->val;
	a.push_back(root->val);
	if (root->left == NULL && root->right == NULL)
	{
		if (sum == target)
		{
			result.push_back(a);
		}
	}
	else
	{
		visit(root->left, target, sum, a, result);
		visit(root->right, target, sum, a, result);
	}
	
	a.pop_back();
}

vector<vector<int> >  fun(Node *root, int target)
{
	vector<vector<int> > result;
	vector<int> a;
	visit(root, target, 0, a, result);
	
	return result;
}