HZAU 1205 Sequence Number（双指针）

#include <cstdio>
#include <vector>
#include <cstring>
#include <string>
#include <cstdlib>
#include <iostream>
#include <map>
#include <cmath>
#include <algorithm>
using namespace std;
typedef long long LL;
typedef pair<int,int>pii;
const int N = 1e5+5;
const double eps = 1e-8;
int T,n,w[N],sum[N<<2],p[N<<2],cnt,m,ret[N];
int k,a[N],mi[N];
int main() {
    while(~scanf("%d",&n)){
 
        int ans=0;
        mi[0]=1e9+10;
        for(int i=1;i<=n;i++){
            scanf("%d",&a[i]);
            mi[i]=1e9+10;
        }
        for(int i=1;i<=n;i++){
            mi[i]=min(mi[i-1],a[i]);
        }
        for(int l=n,r=n;l>=1;l--){
            if(mi[l]>a[r]){
                while(a[r]<mi[l]){
                    r--;
                }
                ans=max(ans,r-l);
            }
            else {
                ans=max(ans,r-l);
            }
        }
        printf("%d\n",ans);
    }
   return 0;
}