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Extra-terrestrial Intelligence

题目背景

注意这题要加上这个：

freopen("input.txt","r",stdin);
freopen("output.txt","w",stdout);

题面翻译

给定一 $01$ 序列，试问其中的 $1$ 是否等距.若等距则输出YES,否则输出NO。 Translated by @稀神探女

input: input.txt

output: output.txt

题目描述

Recently Vasya got interested in finding extra-terrestrial intelligence. He made a simple extra-terrestrial signals’ receiver and was keeping a record of the signals for $n$ days in a row. Each of those $n$ days Vasya wrote a 1 in his notebook if he had received a signal that day and a 0 if he hadn’t. Vasya thinks that he has found extra-terrestrial intelligence if there is a system in the way the signals has been received, i.e. if all the intervals between successive signals are equal. Otherwise, Vasya thinks that the signals were sent by some stupid aliens no one cares about. Help Vasya to deduce from the information given by the receiver if he has found extra-terrestrial intelligence or not.

输入格式

The first line contains integer $n$ ( $3<=n<=100$ ) — amount of days during which Vasya checked if there were any signals. The second line contains $n$ characters 1 or 0 — the record Vasya kept each of those $n$ days. It’s guaranteed that the given record sequence contains at least three 1s.

输出格式

If Vasya has found extra-terrestrial intelligence, output YES, otherwise output NO.

样例 #1

样例输入 #1

8
00111000

样例输出 #1

YES

样例 #2

样例输入 #2

7
1001011

样例输出 #2

NO

样例 #3

样例输入 #3

7
1010100

样例输出 #3

YES