[LC] 1048. Longest String Chain

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".

class Solution {
    public int longestStrChain(String[] words) {
        Arrays.sort(words, (a, b) -> a.length() - b.length());
        // map is used as space for dp best[i] = 1 + best[i- 1]
        Map<String, Integer> map = new HashMap<>();
        int res = 0;
        for (String word: words) {
            map.put(word, 1);
            for (int i = 0; i < word.length(); i++) {
                String prev = word.substring(0, i) + word.substring(i + 1);
                int curLen = map.get(word);
                if (map.containsKey(prev) && map.get(prev) + 1 > curLen) {
                    map.put(word, map.get(prev) + 1);
                }
            }
            res = Math.max(res, map.get(word));
        }
        return res;
    }
}