学步园

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]
]

/**
 * Definition for binary tree
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    vector<vector<int> > pathSum(TreeNode *root, int sum) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        
    	if ( !root )
			return vector<vector<int> >();
		vector<vector<int> > ans;
		vector<int> path;
		solve(root,sum,ans,path);
		return ans;
    }
	void solve(TreeNode* root,int sum,vector<vector<int> >& ans,vector<int>& path)
	{
		if ( !root  )
			return;
		path.push_back(root->val);
		sum-=root->val;

		if ( !root->left && !root->right )
		{
			if (sum==0)
				ans.push_back(path);
		}
		else
		{
			solve(root->left,sum,ans,path);
			solve(root->right,sum,ans,path);
		}
		path.pop_back();
	}

};