CodeForces - 603A-Alternative Thinking (思维题）

Kevin的USAICO竞赛策略

最新推荐文章于 2020-01-17 16:11:09 发布

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最新推荐文章于 2020-01-17 16:11:09 发布

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原文链接：http://www.cnblogs.com/Staceyacm/p/10781924.html

Kevin在USAICO竞赛中成绩不佳，决定通过翻转字符串中的一段子串来优化其成绩，目标是找到最长的交替子序列。文章讨论了如何通过算法解决这一问题，并提供了一段C++代码实现。

Kevin has just recevied his disappointing results on the USA Identification of Cows Olympiad (USAICO) in the form of a binary string of length n. Each character of Kevin's string represents Kevin's score on one of the n questions of the olympiad—'1' for a correctly identified cow and '0' otherwise.

However, all is not lost. Kevin is a big proponent of alternative thinking and believes that his score, instead of being the sum of his points, should be the length of the longest alternating subsequence of his string. Here, we define an alternating subsequence of a string as a not-necessarily contiguous subsequence where no two consecutive elements are equal. For example, {0, 1, 0, 1}, {1, 0, 1}, and {1, 0, 1, 0} are alternating sequences, while {1, 0, 0} and {0, 1, 0, 1, 1} are not.

Kevin, being the sneaky little puffball that he is, is willing to hack into the USAICO databases to improve his score. In order to be subtle, he decides that he will flip exactly one substring—that is, take a contiguous non-empty substring of his score and change all '0's in that substring to '1's and vice versa. After such an operation, Kevin wants to know the length of the longest possible alternating subsequence that his string could have.

Input

The first line contains the number of questions on the olympiad n (1 ≤ n ≤ 100 000).

The following line contains a binary string of length n representing Kevin's results on the USAICO.

Output

Output a single integer, the length of the longest possible alternating subsequence that Kevin can create in his string after flipping a single substring.

Examples

Input

8
10000011

Output

Input

2
01

Output

Note

In the first sample, Kevin can flip the bolded substring '10000011' and turn his string into '10011011', which has an alternating subsequence of length 5: '10011011'.

In the second sample, Kevin can flip the entire string and still have the same score.

找规律即可（虽然也找了好久）

代码：

#include<cstdio>
#include<iostream>
#include<algorithm>
#include<cstring>

using namespace std;

int main()
{
    int n;
    char a[100005];
    cin>>n;
    scanf("%s",a);
    int num=1;
    for(int t=1;t<n;t++)
    {
    	if(a[t]!=a[t-1])
    	{
    		num++;
		}
	}
	if(num+2<n)
	{
		printf("%d\n",num+2);
	}
	else
	{
		printf("%d\n",n);
	}
    return 0; 
}

转载于:https://www.cnblogs.com/Staceyacm/p/10781924.html