全排列next_permutation

要保证a函数为从小到大排序的，所以要用sort

    rep(i,1,n) cin>>a[i];
    sort(a+1,a+1+n);
    do{
        rep(i,1,n){
            cout<<a[i]<<sp;
        }
        cout<<endl;
    }while(next_permutation(a+1,a+1+n));