Uva 11991 Easy Problem from Rujia Liu?

Easy Problem from Rujia Liu?

题目：http://uva.onlinejudge.org/index.php?option=com_onlinejudge&Itemid=8&page=show_problem&category=229&problem=3142&mosmsg=Submission+received+with+ID+12182235

map函数参考： http://hi.baidu.com/0wingbinging/item/48b52423fc00d00177272c0c

#include <iostream>
#include <vector>
#include <stdio.h>
#include <map>

using namespace std;

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