leetcode@ [318] Maximum Product of Word Lengths (Bit Manipulations)

https://leetcode.com/problems/maximum-product-of-word-lengths/

Given a string array words, find the maximum value of length(word[i]) * length(word[j]) where the two words do not share common letters. You may assume that each word will contain only lower case letters. If no such two words exist, return 0.

Example 1:

Given ["abcw", "baz", "foo", "bar", "xtfn", "abcdef"]
Return 16
The two words can be "abcw", "xtfn".

Example 2:

Given ["a", "ab", "abc", "d", "cd", "bcd", "abcd"]
Return 4
The two words can be "ab", "cd".

Example 3:

Given ["a", "aa", "aaa", "aaaa"]
Return 0
No such pair of words.

class Solution {
public:

    void strToBits(vector<int>& bits, vector<string>& words) {
        for(int i=0; i<words.size(); ++i) {
            int tmp = 0;
            for(int j=0; j<words[i].size(); ++j) {
                int offset = words[i][j] - 'a';
                tmp = (tmp | (1 << offset));
            }
            bits[i] = tmp;
        }
    }

    int maxProduct(vector<string>& words) {
        int n = words.size();
        if(n < 2)  return 0;
        
        vector<int> bits(n, 0);
        strToBits(bits, words);
        
        int res = 0;
        for(int i=0; i<n; ++i) {
            for(int j=i+1; j<n; ++j) {
                int len1 = words[i].length(), len2 = words[j].length();
                if((bits[i] & bits[j]) == 0) {
                    res = max(res, len1 * len2);
                }
            }
        }
        
        return res;
    }
};