cf B. Sereja and Suffixes

http://codeforces.com/contest/368/problem/B

从后往前找一遍就可以。

#include <cstdio>
#include <cstring>
#include <algorithm>
#define maxn 200000
using namespace std;

int dp[maxn];
int n,m;
int a[maxn];
bool vis[maxn];

int main()
{
    while(scanf("%d%d",&n,&m)!=EOF)
    {
        memset(dp,0,sizeof(dp));
        memset(vis,false,sizeof(vis));
        int t1=0;
        for(int i=1; i<=n; i++)
        {
            scanf("%d",&a[i]);
        }
        for(int i=n; i>=1; i--)
        {
            if(!vis[a[i]])
            {
                vis[a[i]]=true;
                t1++;
                dp[i]=t1;
            }
            else
            {
                dp[i]=t1;
            }
        }
        for(int i=1; i<=m; i++)
        {
            int x;
            scanf("%d",&x);
            printf("%d\n",dp[x]);
        }
    }
    return 0;
}