1048. Longest String Chain

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Given a list of words, each word consists of English lowercase letters.

Let's say word1 is a predecessor of word2 if and only if we can add exactly one letter anywhere in word1 to make it equal to word2. For example, "abc" is a predecessor of "abac".

A word chain is a sequence of words [word_1, word_2, ..., word_k] with k >= 1, where word_1 is a predecessor of word_2, word_2 is a predecessor of word_3, and so on.

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

Example 1:

Input: ["a","b","ba","bca","bda","bdca"]
Output: 4
Explanation: one of the longest word chain is "a","ba","bda","bdca".

Note:

1. 1 <= words.length <= 1000

2. 1 <= words[i].length <= 16

3. words[i] only consists of English lowercase letters.

Solution

  public int longestStrChain(String[] words) {
        int max = 1;
        int N = words.length;
        Map<String, Integer> map = new HashMap<>();
        Arrays.sort(words, (w1, w2)-> w1.length() - w2.length());
        for(int i = 0; i < N; i++){
           map.put(words[i], 1);

           for(int j = 0; j < words[i].length(); j++){
                String newWord = words[i].substring(0, j) + words[i].substring(j+1);
                map.put(words[i], Math.max(map.get(words[i]),
                                           map.getOrDefault(newWord, 0) + 1 ));
           }
           max = Math.max(max, map.get(words[i]));
        }
        return max;
    }