leetcode Longest Palindromic Substring

想了一晚上，觉得 这基本上是最优解法了。。

string palindromic(string s) {
	int i, i2, j, n = s.length(), tmp;
	if (n < 2 || (n == 2 && s[0] == s[1]))
	{
		return s;
	}
	int max = 0, start = 0;
	for (i = 0; i < n - 1; i++)
	{
		i2 = i;
		while (s[i2] == s[i2 + 1])
		{
			i2++;
		}
		tmp = (max - i2 + i)/2;
		if (i2 + tmp >= n || i - tmp < 0 || s[i2 + tmp] != s[i-tmp])
		{
			i = i2; continue;
		}
		for (j = 1;; j++)
		{
			if (i < j || i2 + j > n - 1 || s[i - j] != s[i2 + j])
			{
				break;
			}
		}
		if (2 * (j - 1) + i2 - i > max)
		{
			max = 2 * (j - 1) + i2 - i;
			start = i - j + 1;
		}
		i = i2;
	}
	return s.substr(start, max + 1);
}