Submission #1792816

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Source Code Expand

#include <bits/stdc++.h>
#define rep(n) for(lint I = 0; (I) < (lint)(n); ++(I))
#define repeat(i, n) for(lint i = 0; (i) < (lint)(n); ++(i))
#define repeat_to(i, n) for(lint i = 0; (i) <= (lint)(n); ++(i))
#define repeat_from(i, m, n) for(lint i = (m); (i) < (lint)(n); ++(i))
#define repeat_from_to(i, m, n) for(lint i = (m); (i) <= (lint)(n); ++(i))
#define repeat_reverse_from_to(i, m, n) for(lint i = (m); (i) >= (lint)(n); --(i))
#define el cout<<endl
#define dump(x) cout<<" "<<#x<<"="<<x
#define vdump(v) for(size_t I=0; I<v.size(); ++I){cout<<" "<<#v<<"["<<I<<"]="<<v[I];} cout<<endl
using namespace std;
using lint = long long;
using ld = long double;

int main(void) {
    int n;
    cin >> n;
    vector<int> p(n);
    repeat(i, n) {
        cin >> p[i];
        --p[i];
    }
    p.push_back(0);
        
    int ans = 0;
    bool closed = true;
    int len = 0;
    repeat(i, n + 1) {
        if (p[i] == i && closed) {
            closed = false;
            ++len;
        }
        else if (p[i] == i && not closed) {
            ++len;
        }
        else if (p[i] != i && not closed) {
            ans += (len + 1) / 2;
            len = 0;
            closed = true;
        }
    }
    cout << ans << endl;
}

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