【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]
]

/**
 * 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>> ret;
        vector<int> path;
        //这里注意判断空树，否则需要在下面的函数里面判断
        if (root != nullptr) {
            pathSum(root, sum, path, ret);   
        }
        return ret;
    }
private:
    void pathSum(TreeNode *node, int target, vector<int> &path, vector<vector<int>> &ret) {
        path.push_back(node->val);
        if (node->left != nullptr) {
            pathSum(node->left, target - node->val, path, ret);
        }
        if (node->right != nullptr) {
            pathSum(node->right, target - node->val, path, ret);
        }
        if (node->left == nullptr && node->right == nullptr) {
            if(node->val == target) {
                ret.push_back(path);
            }
        } 
        path.pop_back();
    }    
};

递归解决