POJ 3320 Jessica's Reading Problem

#include<cstdio>
#include<cstring>
#include<cmath>
#include<queue>
#include<map>
#include<algorithm>
using namespace std;

const int maxn=1000000+10;
int n,size;
int a[maxn];
map<int,int>f;
int ans;

int main()
{
    while(~scanf("%d",&n))
    {
        f.clear(); size=0; ans=n;
        for(int i=1;i<=n;i++)
        {
            scanf("%d",&a[i]);
            if(f[a[i]]==0)
            {
                size++;
                f[a[i]]=1;
            }
        }
        f.clear();
        int l=1,r=1,num=1; f[a[1]]++;
        while(1)
        {
            if(num==size)
            {
                ans=min(ans,r-l+1);
                f[a[l]]--; if(f[a[l]]==0) num--;
                l++;
            }
            else
            {
                if(r==n) break;
                r++;
                f[a[r]]++; if(f[a[r]]==1) num++;
            }
        }
        printf("%d\n",ans);
    }
    return 0;
}