47. Permutations II

题目

Given a collection of numbers that might contain duplicates, return all possible unique permutations.

For example,
[1,1,2] have the following unique permutations:
[
[1,1,2],
[1,2,1],
[2,1,1]
]

解析

题目：对一个数组进行全排列，数组有重复的数字
思路：使用回溯法，用map根据数组的下标进行回溯，在判断结果是去重即可

代码

class Solution {public:    vector<vector<int>> permuteUnique(vector<int>& nums) {        vector<vector<int>> ret;        vector<int> tmp;        unordered_map<int,bool> m;        m[0]=m[1]=m[2]=false;   //数组下标        help(ret,tmp,m,nums);        return ret;    }    void help(vector<vector<int>> &ret,vector<int> &tmp,unordered_map<int,bool> &m,vector<int> &nums){        if(tmp.size()==nums.size()&&find(ret.begin(),ret.end(),tmp)==ret.end()){   //去重            ret.push_back(tmp);            return;        }        for(int i=0;i<nums.size();i++){            if(!m[i]){                tmp.push_back(nums[i]);                m[i]=true;                help(ret,tmp,m,nums);                tmp.pop_back();                m[i]=false;            }        }    }};