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| 1 | +class Solution { |
| 2 | + fun longestStrChain(words: Array<String>): Int { |
| 3 | + val wordSet = words.toSet() |
| 4 | + val memo = mutableMapOf<String, Int>() |
| 5 | + var maxChain = 0 |
| 6 | + for (word in words) { |
| 7 | + maxChain = maxOf(maxChain, dfs(word, wordSet, memo)) |
| 8 | + } |
| 9 | + return maxChain |
| 10 | + } |
| 11 | + |
| 12 | + fun dfs(word: String, wordSet: Set<String>, memo: MutableMap<String, Int>): Int { |
| 13 | + if (word in memo) { |
| 14 | + return memo[word]!! |
| 15 | + } |
| 16 | + var longestChain = 1 |
| 17 | + for (i in word.indices) { |
| 18 | + val predecessor = word.substring(0, i) + word.substring(i + 1) |
| 19 | + if (predecessor in wordSet) { |
| 20 | + longestChain = maxOf(longestChain, dfs(predecessor, wordSet, memo) + 1) |
| 21 | + } |
| 22 | + } |
| 23 | + memo[word] = longestChain |
| 24 | + return longestChain |
| 25 | + } |
| 26 | +} |
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