90分求助，有一个点wa

#include<bits/stdc++.h>
using namespace std;
const long long  maxn=5e7;
long long a[maxn],f[maxn],s[maxn];
long long  n,k;
int main(){
    cin>>n>>k;
    for(int i=1;i<=n;i++){
        cin>>a[i];
    }
    int head=1,tail=0;
    f[++tail]=1;
    for(int i=2;i<=n;i++){
        while(tail>=head&&f[head]<=i-k) head++;
        while(tail>=head&&a[i]<=a[f[tail]]) tail--;
        f[++tail]=i;
        if(i>=k) cout<<a[f[head]]<<" ";
    }
    cout<<endl;
    head=1,tail=0;
    s[++tail]=1;
    for(int i=2;i<=n;i++){
        while(tail>=head&&s[head]<=i-k) head++;
        while(tail>=head&&a[i]>=a[s[tail]]) tail--;
        s[++tail]=i;
        if(i>=k) cout<<a[s[head]]<<" ";
    }
    return 0;
}