Submission #73992697

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Source Code Expand

#include<bits/stdc++.h>
using namespace std;

#define int long long

void solve(){
    
    int n, k; cin >> n >> k;
    vector<int> a(n + 1, 0);

    for(int i = 0; i < n; i++){
        cin >> a[i];
    }

    vector<int> diff(n + 1, 0);
    int ans = 0;
    if(a[0] == 1){
        ans = 1;
        diff[0] = 1;
        diff[k] = -1;
    }
    for(int i = 1; i + k - 1< n; i++){
        diff[i] += diff[i-1];

        if((a[i] + diff[i]) % 2 != 0){
            ans++;
            diff[i] += 1;
            diff[i + k] -= 1;
        }
    }

    for(int i = n - k + 1; i < n; i++){
        diff[i] += diff[i-1];
    }

    for(int i = 1; i < k; i++){
        int idx = n - i;

        if((a[idx] + diff[idx]) % 2 != 0){
            cout << -1 << endl;
            return;
        }
    }

    cout << ans << endl;
}

signed main(){

    ios::sync_with_stdio(false);
    cin.tie(nullptr);

    solve();
}

Submission Info

Judge Result