BZOJ 3831 Little Bird

//要熟练手写队列 
//单调队列优化DP筛选转移点 
#include<bits/stdc++.h>
using namespace std;
const int maxn = 1000010;
int n, qut;
int q[maxn], f[maxn], h[maxn];

inline void getInit(){
    memset(f, 0, sizeof(f));
    memset(q, 0, sizeof(q));
}

inline bool judge(int x, int y){//单调队列优先级，先f因为若f[i]<f[j]，最不济也可以调到j上，然后比h，同样h[i]>=h[j]时可以无伤跳到j上 
    if(f[x] != f[q[y]]) return f[x] < f[q[y]];
    return h[x] >= h[q[y]];
}

int main(){
    scanf("%d", &n);
    for(int i = 1; i <= n; i++)
        scanf("%d", &h[i]);
    scanf("%d", &qut);
    while(qut--){
        getInit();
        int k;
        scanf("%d", &k);
        f[1] = 0;
        int front = 0, tail = 0;
        q[0] = 1;
        for(int i = 2; i <= n; i++){
            while(front <= tail && i - q[front] > k)    front++;
            f[i] = f[q[front]] + (h[q[front]] <= h[i]);
            while(front <= tail && judge(i, tail-1))    tail--;
            q[++tail] = i;//tail是指向最后一个元素的后一个，所以 
        }
        printf("%d\n", f[n]);
    }
    return 0;
}