LeetCode in Kotlin

854. K-Similar Strings

Hard

Strings s1 and s2 are k-similar (for some non-negative integer k) if we can swap the positions of two letters in s1 exactly k times so that the resulting string equals s2.

Given two anagrams s1 and s2, return the smallest k for which s1 and s2 are k-similar.

Example 1:

Input: s1 = “ab”, s2 = “ba”

Output: 1

Explanation: The two string are 1-similar because we can use one swap to change s1 to s2: “ab” –> “ba”.

Example 2:

Input: s1 = “abc”, s2 = “bca”

Output: 2

Explanation: The two strings are 2-similar because we can use two swaps to change s1 to s2: “abc” –> “bac” –> “bca”.

Constraints:

• 1 <= s1.length <= 20
• s2.length == s1.length
• s1 and s2 contain only lowercase letters from the set {'a', 'b', 'c', 'd', 'e', 'f'}.
• s2 is an anagram of s1.

Solution

class Solution {
    fun kSimilarity(a: String, b: String): Int {
        var ans = 0
        val achars = a.toCharArray()
        val bchars = b.toCharArray()
        ans += getAllPerfectMatches(achars, bchars)
        for (i in achars.indices) {
            if (achars[i] == bchars[i]) {
                continue
            }
            return ans + checkAllOptions(achars, bchars, i, b)
        }
        return ans
    }

    private fun checkAllOptions(achars: CharArray, bchars: CharArray, i: Int, b: String): Int {
        var ans = Int.MAX_VALUE
        for (j in i + 1 until achars.size) {
            if (achars[j] == bchars[i] && achars[j] != bchars[j]) {
                swap(achars, i, j)
                ans = Math.min(ans, 1 + kSimilarity(String(achars), b))
                swap(achars, i, j)
            }
        }
        return ans
    }

    private fun getAllPerfectMatches(achars: CharArray, bchars: CharArray): Int {
        var ans = 0
        for (i in achars.indices) {
            if (achars[i] == bchars[i]) {
                continue
            }
            for (j in i + 1 until achars.size) {
                if (achars[j] == bchars[i] && bchars[j] == achars[i]) {
                    swap(achars, i, j)
                    ans++
                    break
                }
            }
        }
        return ans
    }

    private fun swap(a: CharArray, i: Int, j: Int) {
        val temp = a[i]
        a[i] = a[j]
        a[j] = temp
    }
}

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