CodeForces - 645 C.Enduring Exodus

快乐二分

用前缀和随便搞一下

#include <cstdio>
using namespace std;
const int N = ;
int p[N];
int n, k, cnt = ;
inline int msum(int a, int b) {
    if (a < )
        a = ;
    return (b - a - sum[b] + sum[a]);
}

inline bool judge(int s) {
    for (int i = ; i <= n; i++) {
        if (p[i] == )
            continue;
        if (msum(i - s - , i - ) + msum(i, i + s) >= k)
            return true;
    }
    return false;
}

int main() {
    scanf("%d %d", &n, &k);
    for (int i = ; i <= n; i++) {
        scanf("%d", &p[i]);
        sum[i] = sum[i - ] + p[i];
    }
    int l = , r = n /  + ;
    while (l < r) {
        int mid = (l + r) / ;
        if (judge(mid))
            r = mid;
        else
            l = mid + ;
    }
    printf("%d\n", l);
    return ;
}