1. 单词长度的最大乘积
给定一个字符串数组 words，请计算当两个字符串 words[i] 和 words[j] 不包含相同字符时，它们长度的乘积的最大值。假设字符串中只包含英语的小写字母。如果没有不包含相同字符的一对字符串，返回 0。
方法一：

def maxProduct(words):
    map_dict = {}
    n = len(words)
    res = 0
    ascii_A = ord('a')
    for i in range(n):
        temp = 0
        for c in words[i]:
            temp |= 1 << (ord(c) - ascii_A)
        if temp in map_dict:
            map_dict[temp] = max(len(words[i]), map_dict[temp])
        else:
            map_dict[temp] = len(words[i])
    for keyA in map_dict.keys():
        for keyB in map_dict.keys():
            if (keyA & keyB) == 0:
                res = max(res, map_dict[keyA] * map_dict[keyB])
    return res

方法二：

def maxProduct(words):
    n = len(words)
    word_sets = [set(word) for word in words]
    max_product = 0
    for i in range(n):
        for j in range(i + 1, n):
            if all(char not in word_sets[j] for char in word_sets[i]):
                product = len(words[i]) * len(words[j])
                max_product = max(max_product, product)
    return max_product

方法三：

def maxProduct(words):
    n = len(words)
    lengths = [len(word) for word in words]
    bit_representations = []
    for word in words:
        bit_rep = 0
        for char in word:
            bit_rep |= 1 << (ord(char) - ord('a'))
        bit_representations.append(bit_rep)
    max_product = 0
    for i in range(n):
        for j in range(i + 1, n):
            if bit_representations[i] & bit_representations[j] == 0:
                max_product = max(max_product, lengths[i] * lengths[j])
    return max_product