longest-common-prefix

public string LongestCommonPrefix(string[] strs)
{
	if (strs.Length == 0) return null;

	string res = string.Empty;
	string str = strs[0];

	foreach (var s in strs)
	{
		if (s.Length < str.Length)
			str = s;
	}

	int len = strs.Length;

	for (int i = 0; i < str.Length; i++)
	{
		for (int j = 0; j < len; j++)
		{
			if (str[i] == strs[j][i])
				continue;
			else
				return res;
		}

		res += str[i];
	}

	return res;
}