Codeforces #36 A "Extra-terrestrial Intelligence"

問題：http://codeforces.com/contest/36/problem/A

本番．

"1"が同じ間隔で出現するかどうか．
#35の時点でファイル入出力だってわかってたのに同じ過ちを繰り返して提出．

import java.io.File;
import java.io.PrintWriter;
import java.util.Scanner;

public class A_ExtraTerrestrialIntelligence {
	public static void main(String[] args) throws Exception {
		File in = new File("input.txt"), out = new File("output.txt");
		Scanner s;
		PrintWriter pw;
		if (in.exists()) {
			s = new Scanner(in);
			pw = new PrintWriter(out);
		} else {
			s = new Scanner(System.in);
			pw = new PrintWriter(System.out);
		}
		s.next();
		String str = s.next();
		int d = 0;
		String result = "YES";
		for (int i = str.indexOf('1'), j = str.indexOf('1', i + 1); j >= 0; i = j, j = str
				.indexOf('1', i + 1)) {
			if (d == 0 || j - i == d) {
				d = j - i;
			} else {
				result = "NO";
			}
		}
		pw.println(result);
		pw.close();
	}
}