This submission is migrated from previous version of oj.uz, which used different machine for grading. This submission may have different result if resubmitted.
#include <bits/stdc++.h>
using namespace std;
#define pii pair <int, int>
#define fi first
#define se second
#define mp make_pair
#define getbit(x, i) ((x&(1<<i)) != 0)
const int NM = 1000;
int N, S, a[NM+5], idx[NM+5];
vector <pii> ans;
void op(int i, int j){
ans.push_back(mp(i, j));
a[i] ^= a[j];
}
void swaping(int i){
op(i+1, i);
op(i, i+1);
op(i+1, i);
}
bool cmp(int x, int y){
int i = min(x, N-x+1), j = min(y, N-y+1);
if (i != j) return i < j;
return x < y;
}
void solve1(){
for (int i = 1; i <= N; i++)
idx[i] = i;
sort(idx+1, idx+1+N, cmp);
for (int ii = 1; ii <= N; ii++){
int i = idx[ii];
int k = i;
if (ii%2 != 0){
for (int j = i+1; j <= N; j++)
if (a[j] < a[k]) k = j;
for (int j = k-1; j >= i; j--)
swaping(j);
}
else{
for (int j = 1; j < i; j++)
if (a[j] < a[k]) k = j;
for (int j = k+1; j <= i; j++)
swaping(j-1);
}
}
}
void solve2(){
int tar = N+1;
for (int i = 19; i >= 0; i--){
bool ok = 0;
for (int j = 1; j <= N; j++)
if (getbit(a[j], i)){
ok = 1;
break;
}
if (ok == 0) continue;
tar--;
for (int j = 1; j < tar; j++)
if (getbit(a[j], i) && !getbit(a[j+1], i)){
op(j+1, j);
op(j, j+1);
}
else if (getbit(a[j], i) && getbit(a[j+1], i)){
op(j, j+1);
}
}
}
int main(){
ios_base::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
cin >> N >> S;
for (int i = 1; i <= N; i++) cin >> a[i];
if (S == 1) solve1();
else solve2();
cout << ans.size() << '\n';
for (int i = 0; i < ans.size(); i++)
cout << ans[i].fi << ' ' << ans[i].se << '\n';
return 0;
}
Compilation message (stderr)
xorsort.cpp: In function 'int main()':
xorsort.cpp:85:20: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<std::pair<int, int> >::size_type' {aka 'long unsigned int'} [-Wsign-compare]
85 | for (int i = 0; i < ans.size(); i++)
| ~~^~~~~~~~~~~~
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