USACO Section 1.1 Broken Necklace

/*
ID: lucien23
PROG: beads
LANG: C++
*/

#include<iostream>
#include<fstream>
#include<string>
#include<map>
using namespace std;

int main()
{
	ifstream infile("beads.in");
	ofstream outfile("beads.out");
	if(!infile || !outfile)
	{
		cout<<"file operation failure!"<<endl;
		return -1;
	}
	int N;
	string nacklace;
	infile>>N>>nacklace;
	int maxNum=0;
	int i=0,right,left;
	char lPivot,rPivot;
	while(i<N)
	{
		rPivot=nacklace[i];
		right=i+1;
		while(right<2*N && right%N!=i)
		{
			if(rPivot=='w')
				rPivot=nacklace[right%N];
			if(nacklace[right%N]!='w' && nacklace[right%N]!=rPivot)
				break;
			right++;
		}
		
		//得先判断i-1是否有效
		if(right-i==N)
		{
			maxNum=N;
			break;
		}

		left=i-2+N;
		lPivot=nacklace[(left+1)%N];
		while (left>=0 && !(left>=i && left<right))
		{
			if(lPivot=='w')
				lPivot=nacklace[left%N];
			if(nacklace[left%N]!='w' && nacklace[left%N]!=lPivot)
				break;
			left--;
		}

		int num=right-left+N-1;
		if(num>maxNum)
		{
			maxNum=num;
		}
		cout<<"i="<<i<<" left="<<left<<" right="<<right<<" num="<<num<<endl;
		i=right;
	}

	outfile<<maxNum<<endl;

	return 0;
}