Luogu P1886 滑動窗口

傳送門

此題為單調隊列入門題。單調隊列，可以\(O(n)\)求一段數列中區間極值。記錄隊列中元素大小與該元素在原數組中的位置。當隊首元素超出當前求值區間時，頭指針加一；當當前將入隊元素大於或小於尾元素時，尾指針減一，直到不符合上一條件時，將當前元素入隊。然後要求極值只需輸出隊首元素即可。

#include <cstdio>
const int MAXN = 1000001;
int n, k;
int a[MAXN], que[MAXN], id[MAXN], head, tail;
int main() {
    scanf("%d%d"
 
, &n, &k);
    for (int i = 1; i <= n; ++i)
        scanf("%d", &a[i]);
    head = 1; tail = 0;
    for (int i = 1; i <= n; ++i) {
        while(head <= tail && id[head] <= i - k) head++;
        while(head <= tail && que[tail] >= a[i]) tail--;
        que[++tail] = a[i]; id[tail] = i;
        if
 
(i >= k) printf("%d ", que[head]);
    }
    printf("\n");
    head = 1; tail = 0;
    for (int i = 1; i <= n; ++i) {
        while(head <= tail && id[head] <= i - k) head++;
        while(head <= tail && que[tail] <= a[i]) tail--;
        que[++tail] = a[i]; id[tail] = i;
        if
 
(i >= k) printf("%d ", que[head]);
    }
    printf("\n");
    return 0;
}

[Luogu] P1886 滑動窗口