hihocoder1032 最长回文子串

题目链接：http://hihocoder.com/problemset/problem/1032

推荐讲解博客：https://segmentfault.com/a/1190000003914228

#include <iostream>
#include <string>
#include <cstring>

#define MAX_N 2000005

using namespace std;

int RL[MAX_N]; // RL[i] : 以i为中心的回文半径的值 

void convert( string& str ) {
	string newstr = "#";
	for ( int i = 0, len = str.size() ; i < len ; ++ i ) {
		newstr += str[i];
		newstr += "#";
	}
	str = newstr;
}

int main()
{
	int n;
	string str, nstr;
	cin >> n;
	while ( n -- ) {
		memset( RL, 0, sizeof(RL) );
		cin >> str;
		// 统一处理插入了特殊字符  
		convert(str);
//		cout << str << endl;
		int MaxRight = 0;
		int pos = 0;
		int MaxLen = 0;
		for ( int i = 0, len = str.size() ; i < len ; ++ i ) {
			// 防止重复匹配 
			if ( i < MaxRight ) {
				RL[i] = min(RL[2*pos-i], MaxRight-i);
			} else {
				RL[i] = 1;
			} 
			// 尝试扩展 注意边界 防止越界 
			while ( i-RL[i]>=0 && i+RL[i]<=len && str[i-RL[i]]==str[i+RL[i]] ) RL[i] ++;
			if ( RL[i]+i-1 > MaxRight ) {
				MaxRight = RL[i]+i-1;
				pos = i;
			} 
			// 更新结果 
			if ( MaxLen < RL[i] ) MaxLen = RL[i];
		}
		cout << MaxLen-1 << endl;
	}
	
	return 0;
}