14. Longest Common Prefix

class Solution(object):
    def longestCommonPrefix(self, strs):
        """
        :type strs: List[str]
        :rtype: str
        """
        if not strs:
            return ‘‘
        length = len(strs[0])
        common_prefix = [‘‘]
        chars_at_idx = set()

        for idx in range(length):
            for one_string in strs:
                if len(one_string) <= idx:
                    return ‘‘.join(common_prefix)
                chars_at_idx.add(one_string[idx])
            if len(chars_at_idx) != 1:
                return ‘‘.join(common_prefix)
            common_prefix.append(chars_at_idx.pop())

        return ‘‘.join(common_prefix)

class Solution(object):
    def longestCommonPrefix(self, strs):
        """
        :type strs: List[str]
        :rtype: str
        """
        if not strs:
            return ‘‘
        length = len(strs[0])

        for idx in range(length):
            char = strs[0][idx]
            for one_string in strs:
                if len(one_string) <= idx or one_string[idx] != char:
                    return one_string[:idx]
        return strs[0]