[LeetCode] 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]
]

思路：  参考资料https://leetcode.com/discuss/45131/12ms-11-lines-c-solution
　　　　时间复杂度O(n),空间复杂度O(lgN)

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/**
 * 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) {
        vector<vector<int> > result;
        if (root == NULL) 
            return result;
            
        vector<int> path;
        pathSum(root, sum, result, path);
        
        return result;
    }
    
    void pathSum(TreeNode *root, int sum, vector<vector<int> > &result, vector<int> &path) {
        path.push_back(root->val);
        
        if (root->left == NULL && root->right == NULL) {
            if (root->val == sum) {
                result.push_back(path);
            } 
        } 
        
        if (root->left) 
            pathSum(root->left, sum - root->val, result, path);
            
        if (root->right)
            pathSum(root->right, sum - root->val, result, path);
        
        path.pop_back();
            
    }
};