Problem_318. Maximum Product of Word Lengths - xwu36/LeetCode GitHub Wiki

Problem:

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.

Algorithm:

Use bit to mark the occurred character.
like adc, a means shift left by 1 bit, d means shift left by 4 bit,
so, we can use 01101 to represent adc

Code:

class Solution {
    public int maxProduct(String[] words) {
        if(words == null || words.length == 0)
            return 0;
        int n = words.length;
        int[] counters = new int[n];
        for(int i = 0; i < n; i++){
            String word = words[i];
            counters[i] = 0;
            for(int j = 0; j < word.length(); j++){
                counters[i] |= 1 << (word.charAt(j) - 'a');
            }
        }
        int maxProduct = 0;
        for(int i = 0; i < n; i++){
            for(int j = i + 1; j < n; j++){
                if((counters[i] & counters[j]) == 0 && (words[i].length() * words[j].length() > maxProduct))
                    maxProduct = words[i].length() * words[j].length();
            }
        }
        return maxProduct;
    }
}