LeetCode 1239. Maximum Length of a Concatenated String with Unique Characters

原题链接在这里：https://leetcode.com/problems/maximum-length-of-a-concatenated-string-with-unique-characters/

题目：

Given an array of strings arr. String s is a concatenation of a sub-sequence of arr which have unique characters.

Return the maximum possible length of s.

Example 1:

Input: arr = ["un","iq","ue"]
Output: 4
Explanation: All possible concatenations are "","un","iq","ue","uniq" and "ique".
Maximum length is 4.

Example 2:

Input: arr = ["cha","r","act","ers"]
Output: 6
Explanation: Possible solutions are "chaers" and "acters".

Example 3:

Input: arr = ["abcdefghijklmnopqrstuvwxyz"]
Output: 26

Constraints:

• 1 <= arr.length <= 16
• 1 <= arr[i].length <= 26
• arr[i] contains only lower case English letters.

题解：

In the arr, s could contain duplicate character. These strings with duplicate characters can't be used.

Have a list to maintain all previous bit masks. When checking a new string s, check all previous bit masks, if there is not intersection, then s could be used.

Update the maximum result and add the new bitmast into list.

Time Complexity: expontential. 

Space: expontential.

AC Java:

class Solution {
    public int maxLength(List<String> arr) {
        int res = 0;
        List<Integer> candidates = new ArrayList<>();
        candidates.add(0);
        
        for(String s : arr){
            int dup = 0;
            int sBit = 0;
            for(char c : s.toCharArray()){
                dup |= sBit & 1<<(c-'a');
                sBit |= 1<<(c-'a');
            }
            
            if(dup > 0){
                continue;
            }
            
            for(int i = 0; i<candidates.size(); i++){
                if((candidates.get(i) & sBit) > 0){
                    continue;
                }
                
                candidates.add(candidates.get(i) | sBit);
                res = Math.max(res, Integer.bitCount(candidates.get(i) | sBit));
            }
        }
        
        return res;
    }
}