Yet Another Contest 8 P1 - Permutation Sorting

    1#include <bits/stdc++.h>
    2using namespace std;
    3using ll = long long;
    4using i128 = __int128;
    5const int inf = 1e9;
    6const long long INF = 1e17; //❄️
    7int main() {
    8    ios::sync_with_stdio(0); cin.tie(0); 
    9    int n; cin >> n;
    10    vector<int> v(n + 1), pos(n + 1);
    11    for (int i = 1; i <= n; i++) {
    12        cin >> v[i];
    13        pos[v[i]] = i;
    14    }
    15    vector<int> diff(n + 1);
    16    for (int i = 1; i <= n; i++) {
    17        if (pos[i] != i) {
    18            int l = min(i, pos[i]), r = max(i, pos[i]);
    19            diff[l]++;
    20            diff[r + 1]--;
    21        }
    22    }
    23    int ans = 0;
    24    for (int i = 1; i <= n; i++) {
    25        diff[i] += diff[i - 1];
    26        if (diff[i] > 0) ans++;
    27    }
    28    cout << ans << '\n';
    29    return 0;
    30}