2217 - Collecting Numbers II.cpp

/*
Problem Name: Collecting Numbers II
Problem Link: https://cses.fi/problemset/task/2217
Author: Sachin Srivastava (mrsac7)
*/
#include<bits/stdc++.h>
using namespace std;

#define int long long
#define endl '\n'

signed main(){
    ios_base::sync_with_stdio(false);cin.tie(0);cout.tie(0);
    #ifdef LOCAL
    freopen("input.txt", "r" , stdin);
    freopen("output.txt", "w", stdout);
    #endif
    
    int n,m; cin>>n>>m;
    int l = 1;
    int ind[n+2] = {0}, a[n+1] = {0};
    ind[n+1] = n+1;
    for (int i = 1; i <= n; i++) {
		int x; cin>>x;
		ind[x] = i;
		a[i] = x;
    }
    int c = 1;
    for (int i = 1; i <= n; i++) {
		if (l > ind[i]) 
		c++;
		l = ind[i];
    }
    while(m--) {
		int x,y; cin>>x>>y;
		int r = a[x], s = a[y];
		swap(a[x], a[y]);
		if (ind[r-1] <= ind[r] && ind[r-1] > y) c++;
		if (ind[r-1] > ind[r] && ind[r-1] <= y) c--;
		if (ind[r] <= ind[r+1] && y > ind[r+1]) c++;
		if (ind[r] > ind[r+1] && y <= ind[r+1]) c--;		
		ind[r] = y;
		if (ind[s-1] <= ind[s] && ind[s-1] > x) c++;
		if (ind[s-1] > ind[s] && ind[s-1] <= x) c--;
		if (ind[s] <= ind[s+1] && x > ind[s+1]) c++;
		if (ind[s] > ind[s+1] && x <= ind[s+1]) c--;	
		ind[s] = x;
		cout<<c<<endl;
    }
}