USACO 2017 January Contest, Silver Problem 3. Secret Cow Code

原题下载

USACO2017-JAN-S3

答案:

import java.io.*;
import java.util.*;
public class cowcode {
public static void main(String[] args) throws IOException {
BufferedReader br = new BufferedReader(new FileReader("cowcode.in"));
PrintWriter pw = new PrintWriter(new BufferedWriter(new FileWriter("cowcode.out")));
StringTokenizer st = new StringTokenizer(br.readLine());
String s = st.nextToken();
long index = Long.parseLong(st.nextToken());
pw.println(parse(s, index-1));
pw.close();
}

public static char parse(String s, long index) {
if(index < s.length()) {
return s.charAt((int)index);
}
long length = s.length();
while(2*length <= index) {
length *= 2;
}
if(length == index) {
return parse(s, length-1);
}
return parse(s, index - length - 1);
}
}