NewCoder #提高组 Contest 1 A. 中位数

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题意

求序列中长度>=len的连续子序列的中位数的最大值

题解

二分，枚举答案并检查是否可行

调试记录

无

#include <cstdio>
#include <algorithm>
#define INF 0x3f3f3f3f
#define maxn 100005

using namespace std;

int n, len, a[maxn], sum[maxn];

bool check(int mid){
	sum[0] = 0;
	for (int i = 1; i <= n; i++)
		sum[i] = sum[i - 1] + ((a[i] >= mid) ? 1 : -1);
	
	int Min = INF;
	for (int i = len; i <= n; i++){
		Min = min(Min, sum[i - len]);
		if (sum[i] - Min > 0) return true;
	}
	return false;
}

int main(){
	scanf("%d%d", &n, &len);
	for (int i = 1; i <= n; i++) scanf("%d", &a[i]);
	
	int l = 1, r = INF, ans; 
	
	while (l <= r){
		int mid = (l + r) >> 1;
		if (check(mid)) l = mid + 1, ans = mid;
		else r = mid - 1;
	}
	printf("%d\n", ans);
	
	return 0;
}