POJ Problem 3931 Classmates题解

类似于约瑟夫环问题，输入Mike的编号m和在环中剩余的人数k（包含Mike），求解Mike最少有多少名同学。



#include<iostream>
using namespace std;
typedef long long LL;
LL joseph(LL m, LL k){
if(m == 1) return 2*k-1;
else if(m%2 == 0){
LL n = m/2-1+k;
if(n >= m) return n;
else return 0;
}
else{
LL n1 = joseph((m+1)/2, k)*2;
LL n2 = joseph((m-1)/2, k)*2+1;
if(n2 == 1) n2 = 0;
if(n1 > 0 && n2 > 0)
return min(n1, n2);
else
return max(n1, n2);
}
}

int main(){
LL m, k;
while(cin >> m >> k){
if(m == 0 && k == 0) break;
LL ans = joseph(m, k);
if(ans > 0)
cout << ans << endl;
else
cout << "Impossible" << endl;
}
return 0;
}