UVA 11991 Easy Problem from Rujia Liu?

STL数据结构（vector，map）基本操作

 

#include <iostream>
#include <cstring>
#include <cstdio>
#include <algorithm>
#include <vector>
#include <map>
using namespace std;

int main (){
    int n,m;
    map <int,vector<int> > x;
    while (~scanf ("%d%d",&n,&m)){
        x.clear() ;
        for (int i=1;i<=n;i++){
            int a;
            scanf ("%d",&a);
            if (!x.count (a))       //判断是否为空；
                x[a]=vector<int> {};
            x[a].push_back (i);
        }
        while (m--){
            int k,v;
            scanf ("%d%d",&k,&v);//cout<<x[v][k-1]<<endl;
            if (!x.count(v)||x[v].size()<k)
                printf ("0\n");
            else printf ("%d\n",x[v][k-1]);
        }
    }
    return 0;
}