LeetCode 46. Permutations

题目描述:

Given a collection of distinct numbers, return all possible permutations.

For example,

[1,2,3] have the following permutations:
[
  [1,2,3],
  [1,3,2],
  [2,1,3],
  [2,3,1],
  [3,1,2],
  [3,2,1]
]

使用递归来创建所有排列.

class Solution {
    vector<vector<int>> ret;
    int numsLen;
public:
    vector<vector<int>> permute(vector<int>& nums) {
        vector<bool> flag(nums.size(), false);
        vector<int> p;
        numsLen = nums.size();
        for(int i = 0; i < numsLen; i++){
            flag[i] = true;
            p.push_back(nums[i]);
            permute(nums, flag, p, nums.size() - 1);
            p.pop_back();
            flag[i] = false;
        }
        return ret;
    }
    
    void permute(vector<int>& nums, vector<bool> &flag, vector<int> &p, int lastLen){
        if(lastLen == 0){
            ret.push_back(p);
            return;
        }
        for(int i = 0; i < numsLen; i++){
            if(flag[i]) continue;
            flag[i] = true;
            p.push_back(nums[i]);
            permute(nums, flag, p, lastLen - 1);
            p.pop_back();
            flag[i] = false;
        }
    }
};