LeetCode-in-Java

1048. Longest String Chain

Medium

You are given an array of words where each word consists of lowercase English letters.

wordA is a predecessor of wordB if and only if we can insert exactly one letter anywhere in wordA without changing the order of the other characters to make it equal to wordB.

• For example, "abc" is a predecessor of "abac", while "cba" is not a predecessor of "bcad".

A word chain is a sequence of words [word1, word2, ..., wordk] with k >= 1, where word1 is a predecessor of word2, word2 is a predecessor of word3, and so on. A single word is trivially a word chain with k == 1.

Return the length of the longest possible word chain with words chosen from the given list of words.

Example 1:

Input: words = [“a”,”b”,”ba”,”bca”,”bda”,”bdca”]

Output: 4

Explanation: One of the longest word chains is [“a”,”ba”,”bda”,”bdca”].

Example 2:

Input: words = [“xbc”,”pcxbcf”,”xb”,”cxbc”,”pcxbc”]

Output: 5

Explanation: All the words can be put in a word chain [“xb”, “xbc”, “cxbc”, “pcxbc”, “pcxbcf”].

Example 3:

Input: words = [“abcd”,”dbqca”]

Output: 1

Explanation: The trivial word chain [“abcd”] is one of the longest word chains. [“abcd”,”dbqca”] is not a valid word chain because the ordering of the letters is changed.

Constraints:

• 1 <= words.length <= 1000
• 1 <= words[i].length <= 16
• words[i] only consists of lowercase English letters.

Solution

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

@SuppressWarnings("unchecked")
public class Solution {
    public int longestStrChain(String[] words) {
        List[] lenStr = new List[20];
        for (String word : words) {
            int len = word.length();
            if (lenStr[len] == null) {
                lenStr[len] = new ArrayList<String>();
            }
            lenStr[len].add(word);
        }
        Map<String, Integer> longest = new HashMap<>();
        int max = 0;
        for (String s : words) {
            max = Math.max(findLongest(s, lenStr, longest), max);
        }
        return max;
    }

    public int findLongest(String word, List<String>[] lenStr, Map<String, Integer> longest) {
        if (longest.containsKey(word)) {
            return longest.get(word);
        }
        int len = word.length();
        List<String> words = lenStr[len + 1];
        if (words == null) {
            longest.put(word, 1);
            return 1;
        }
        int max = 0;
        int i;
        int j;
        for (String w : words) {
            i = 0;
            j = 0;
            while (i < len && j - i <= 1) {
                if (word.charAt(i) == w.charAt(j++)) {
                    ++i;
                }
            }
            if (j - i <= 1) {
                max = Math.max(findLongest(w, lenStr, longest), max);
            }
        }
        ++max;
        longest.put(word, max);
        return max;
    }
}

This site is open source. Improve this page.