http://acm.nefu.edu.cn/JudgeOnline/problemshow.php?problem_id=553

#include <iostream>
#include <cstdio>
#include <algorithm>
using namespace std;
const int maxn=1e4;
int data[maxn];
int main()
{
    int m,k;
    while(~scanf("%d%d",&m,&k))
    {
        for(int i=0; i<m; i++)
         scanf("%d",&data[i]);
        sort(data,data+m) ;
        int sum=data[m-k]-data[k-1];
        if(sum&1)
            puts("A");
        else
            puts("B");
    }
    return 0;
}