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