Q9.4 Write a method that returns all subsets of a set.

#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;

void dfs(const vector<int> &s, int start, vector<int> &path, vector<vector<int> > &res) {
if (start == s.size()) {
res.push_back(path);
return ;
}
for (int i = start; i < s.size(); i++) {
path.push_back(s[i]);
dfs(s, i+1, path, res);
path.pop_back();
}
res.push_back(path);
return ;
}

vector<vector<int> > subsets(vector<int> &A) {
vector<vector<int> > res;
if (A.size() == 0) {
return res;
}
vector<int> cur;
dfs(A, 0, cur, res);
return res;
}

void printResult(vector<vector<int> > &res) {
for (int i = 0; i < res.size(); i++) {
cout<<"[";
for (int j = 0; j <res[i].size(); j++) {
cout<<res[i][j];
if (j != res[i].size()-1) {
cout<<",";
}
}
cout<<"]"<<endl;
}
}

void dfs2(const vector<int> &s, int start, vector<int> &path, vector<vector<int> > &res) {
if (start == s.size()) {
res.push_back(path);
return ;
}
int prev = s[start]+1;
for (int i = start; i < s.size(); i++) {
if (prev == s[i]) {
continue;
}
prev = s[i];
path.push_back(s[i]);
dfs2(s, i+1, path, res);
path.pop_back();
}
res.push_back(path);
return ;
}

//如果存在重复元素
vector<vector<int> > subsetsWithDup(vector<int> &S) {
sort(S.begin(), S.end());
vector<vector<int> > res;
vector<int> path;
dfs2(S, 0, path, res);
return res;
}

int main() {
vector<int> A;
for (int i = 1; i <= 3; i++) {
A.push_back(i);
}
vector<vector<int> > res = subsets(A);
printResult(res);
cout<<endl;
A[2] = 2;
res = subsetsWithDup(A);
printResult(res);
return 0;
}