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;
}
}
}
};