#include "sorting.h"
#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define pi pair<int, int>
#define pl pair<ll, ll>
#define vi vector<int>
#define vl vector<ll>
#define fi first
#define se second
#define pb push_back
#define all(x) (x).begin(),(x).end()
bool check(int n, int s[], int r, int x[], int y[], int p[], int q[]) {
for (int i=0; i<r; i++) {
swap(s[x[i]],s[y[i]]);
swap(s[p[i]],s[q[i]]);
}
bool ok=1;
for (int i=0; i<n; i++) {
ok&=(s[i]==i);
}
return ok;
}
int solve(int n, int s[], int m, int x[], int y[], int p[], int q[]) {
if (n==1) {
return 0;
}
int ss[n];
for (int i=0; i<n; i++) {
ss[i]=s[i];
}
vi goesto(n);
iota(all(goesto),0);
for (int i=m-1; i>=0; i--) {
swap(goesto[x[i]],goesto[y[i]]);
}
vi to(n);
vi getpos(n);
for (int i=0; i<n; i++) {
to[goesto[i]]=i;
getpos[s[i]]=i;
}
int ind=0;
for (int i=0; i<n; i++) {
swap(s[x[ind]],s[y[ind]]);
swap(getpos[s[x[ind]]],getpos[s[y[ind]]]);
swap(goesto[x[ind]],goesto[y[ind]]);
swap(to[goesto[x[ind]]],to[goesto[y[ind]]]);
if (s[to[i]]==i) {
swap(s[x[ind]],s[y[ind]]);
swap(getpos[s[x[ind]]],getpos[s[y[ind]]]);
swap(goesto[x[ind]],goesto[y[ind]]);
swap(to[goesto[x[ind]]],to[goesto[y[ind]]]);
continue;
}
p[ind]=to[i];
q[ind]=getpos[i];
swap(s[p[ind]],s[q[ind]]);
swap(getpos[s[p[ind]]],getpos[s[q[ind]]]);
ind++;
if (ind>m) {
return -1;
}
}
for (int i=ind; i<m; i++) {
p[i]=0;
q[i]=0;
}
if (!check(n,ss,m,x,y,p,q)) {
return -1;
}
return m;
}
int findSwapPairs(int n, int s[], int m, int x[], int y[], int p[], int q[]) {
int ans=1e9;
int l=0,r=m;
while (l<=r) {
int mm=l+(r-l)/2;
int ss[n];
for (int i=0; i<n; i++) {
ss[i]=s[i];
}
int *pp=(int*)malloc(sizeof(int)*(unsigned int)mm), *qq=(int*)malloc(sizeof(int)*(unsigned int)mm);
int t=solve(n,ss,mm,x,y,pp,qq);
if (t==-1) {
l=mm+1;
}
else {
for (int i=0; i<t; i++) {
p[i]=pp[i];
q[i]=qq[i];
}
ans=t;
r=t-1;
}
}
assert(check(n,s,ans,x,y,p,q));
return ans;
}
