#include "sorting.h"
#include <iostream>
#include <vector>
#include <cassert>
int const nmax = 1000000;
int init[1 + nmax], n;
int v[1 + nmax], frec[1 + nmax], f[1 + nmax];
int xswap[1 + nmax], yswap[1 + nmax];
int pswap[1 + nmax], qswap[1 + nmax];
void solve(int pos, int &steps){
if(pos == v[pos])
return ;
int oth = v[pos];
pswap[steps] = pos;
qswap[steps] = oth;
std::swap(v[pos], v[oth]);
frec[v[pos]] = pos;
frec[v[oth]] = oth;
steps++;
solve(pos, steps);
}
bool tryit(int target){
for(int i = 0; i < n; i++)
v[i] = init[i];
for(int i = 0; i < target; i++)
std::swap(v[xswap[i]], v[yswap[i]]);
for(int i = 0; i < n; i++)
frec[v[i]] = i;
for(int i = 0; i < n; i++)
f[i] = i;
int steps = 0;
for(int i = 0; i < n; i++)
solve(i, steps);
if(target < steps)
return false;
while(steps < target) {
pswap[steps] = qswap[steps] = 0;
steps++;
}
for(int i = target - 1;0 <= i; i--){
pswap[i] = f[pswap[i]];
qswap[i] = f[qswap[i]];
std::swap(f[xswap[i]], f[yswap[i]]);
}
for(int i = 0; i < n; i++)
assert(i == v[i]);
return true;
}
int binarysearch(int from, int to){
if(from < to){
int mid = (from + to) / 2;
if(tryit(mid))
return binarysearch(from, mid);
else
return binarysearch(mid + 1, to);
} else
return from;
}
int findSwapPairs(int N_, int S_[], int M, int X_[], int Y_[], int P[], int Q[]) {
n = N_;
for(int i = 0; i < n; i++)
init[i] = S_[i];
for(int i = 0; i < M; i++)
xswap[i] = X_[i];
for(int i = 0; i < M; i++)
yswap[i] = Y_[i];
int steps = binarysearch(0, M);
tryit(steps);
for(int i = 0; i < steps; i++)
P[i] = pswap[i];
for(int i = 0; i < steps; i++)
Q[i] = qswap[i];
return steps;
}
