给定一个字符串数组 words，找到 length(word[i]) * length(word[j]) 的最大值，并且这两个单词不含有公共字母。你可以认为每个单词只包含小写字母。如果不存在这样的两个单词，返回 0。

示例 1:

输入: ["abcw","baz","foo","bar","xtfn","abcdef"]
输出: 16 
解释: 这两个单词为 "abcw", "xtfn"。

示例 2:

输入: ["a","ab","abc","d","cd","bcd","abcd"]
输出: 4 
解释: 这两个单词为 "ab", "cd"。

示例 3:

输入: ["a","aa","aaa","aaaa"]
输出: 0 
解释: 不存在这样的两个单词。

代码

class Solution {
public:
    int maxProduct(vector<string>& words) {
        int res = 0;
        vector<int> mask(words.size(), 0);
        for (int i = 0; i < words.size(); ++i) {
            for (char c : words[i]) {
                mask[i] |= 1 << (c - 'a');
            }
            for (int j = 0; j < i; ++j) {
                if (!(mask[i] & mask[j])) {
                    res = max(res, int(words[i].size() * words[j].size()));
                }
            }
        }
        return res;
    }
};