[JS] Longest String Chain

🔒 문제 (LeetCode 1048)

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.

Constraints:

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

 

🌊 입출력

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.

 

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🔑 해결

🌌 알고리즘 - DP

/**
 * @param {string[]} words
 * @return {number}
 */
var longestStrChain = function(words) {
    words.sort((a, b) => a.length - b.length) // predecessor 찾기 위해 길이 순으로 정렬
    let dp = {} // word - word를 만들 수 있는 word chain의 최대 길이
    
    for(const word of words) {
        let max = 0;
        for(let i = 0; i < word.length; i++) {
            // predecessor가 words에 존재하면 기존 chain + 1
            // 그렇지 않으면 새로운 chain 시작
            const pre = word.slice(0, i) + word.slice(i+1)
            max = Math.max(max, (dp[pre] || 0) + 1)
        }
        dp[word] = max
    }
    
    return Math.max(...Object.values(dp))
};