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/*
#include <iostream>
#include <vector>
using namespace std;

vector<bool> vib;
vector<int> vires;
void dfs(vector<int> &vi,int ct){
    if(ct>=vi.size()){
        for(auto ieh: vires)
            cout<<ieh<<" ";
        cout<<endl;
        return ;
    }
    for(int i=0;i<vi.size();++i){
        if(vib[i]==false){
            vib[i]=true;
            vires.push_back(vi[i]);
            dfs(vi,ct+1);
            vires.pop_back();
            vib[i]=false;
        }
    }
}

int main(){
    vector<int> vi;
    vi={1,2,3};
    for(int i=0;i<vi.size();++i)
        vib.push_back(false);
    dfs(vi,0);
    return 0;
}
*/

//这个交换元素的版本更加简洁。
#include <iostream>
#include <vector>
using namespace std;

void exchange(vector<int> &vi, int start){
    if(start>=vi.size()){
        for(auto ieh: vi)
            cout<<ieh<<" ";
        cout<<endl;
    }
    for(int i=start;i<vi.size();++i){
        swap(vi[start],vi[i]);
        exchange(vi, start+1);
        swap(vi[i],vi[start]);
    }
}

int main(){
    vector<int> vi;
    vi={1,2,3};
    exchange(vi, 0);
    return 0;
}