如题：代码返回最大的回文子串，长度一样返回第一个。

空间效率O(1)

时间效率O(N)（一边遍历搞定）

#include <stdio.h>

char* answer;

char* maxPalindrome( const char *s )
{
	bool hasStart = false;
	int startPos = 0, max = 1, maxStart = 0, maxEnd = 0;
	for( int i=1; s[i]!='\0'; i++ )
	{
		if( !hasStart )
		{
			if( s[startPos]==s[i] )
			{
				if( i-startPos>max )
				{
					max = i-startPos;
					maxStart = startPos;
					maxEnd = i;
				}
				continue;
			}
		}

		if( startPos>0 && s[startPos-1]==s[i] ) //李文文指出此处要先检查startPos>0
		{
			startPos--;
			hasStart = true;
		}
		else
		{
			if( hasStart==true )
				startPos = --i;
			else
				startPos = i;
			hasStart = false;
		}

		if( startPos<=0 || i-startPos+1>max )
		{
			max = i-startPos;
			maxStart = startPos;
			maxEnd = i;
		}
	}

	int length = maxEnd-maxStart+1;
	answer = new char[length+1];
	for( int i=0; i<length; i++ )
	{
		answer[i] = s[i+maxStart];
	}
	answer[length] = '\0';
	return answer;
}



int main()
{
	char s[10][100] = { 
		"aigbcddcbgaaaaaaaa",
		"aigbcddcbggggggggg",
		"aaaaa",
		"aaaaaa",
		"aaaaaaaigbcddcbgiaaaaaaa",
		"a"
	};
	
	for( int i=0; i<6; i++ )
		printf( "%s\n", maxPalindrome(s[i]) );
}

这个自己理解吧，我也不多说了没什么难度。欢迎反馈各种错误 输入例子。