Merge pull request ByteByteGoHq#2 from Destiny-02/main

Add Next Lexicographical Sequence

Author: marttp

kotlin/src/main/kotlin/common/twopointers/nextlexicographicalsequence/NextLexicographicalSequence.kt

@@ -0,0 +1,39 @@
+package common.twopointers.nextlexicographicalsequence
+
+class NextLexicographicalSequence {
+
+    fun solution(s: String): String {
+        val letters = s.toCharArray()
+
+        // Locate the pivot, which is the first character from the right that breaks
+        // non-increasing order. Start searching from the second-to-last position,
+        // since the last character is neither increasing nor decreasing.
+        var pivot = letters.size - 2
+        while (pivot >= 0 && letters[pivot] >= letters[pivot + 1]) {
+            pivot--
+        }
+
+        // If pivot is not found, the string is already in its largest permutation. In
+        // this case, reverse the string to obtain the smallest permutation.
+        if (pivot == -1) {
+            letters.reverse()
+            return letters.joinToString("")
+        }
+
+        // Find the rightmost successor to the pivot.
+        var rightmostSuccessor = letters.size - 1
+        while (letters[rightmostSuccessor] <= letters[pivot]) {
+            rightmostSuccessor--
+        }
+
+        // Swap the rightmost successor with the pivot to increase the lexicographical
+        // order of the suffix.
+        letters[pivot] = letters[rightmostSuccessor].also { letters[rightmostSuccessor] = letters[pivot] }
+
+        // Reverse the suffix after the pivot to minimize its permutation.
+        val suffix = letters.sliceArray(pivot + 1 until letters.size)
+        suffix.reverse()
+
+        return (letters.sliceArray(0..pivot) + suffix).joinToString("")
+    }
+}

kotlin/src/test/kotlin/common/twopointers/nextlexicographicalsequence/NextLexicographicalSequenceTest.kt

@@ -0,0 +1,19 @@
+package common.twopointers.nextlexicographicalsequence
+
+import org.junit.jupiter.api.Test
+import kotlin.test.assertEquals
+
+class NextLexicographicalSequenceTest {
+
+    private val question = NextLexicographicalSequence()
+
+    @Test
+    fun `Verify solution`() {
+        assertEquals("a", question.solution("a"))
+        assertEquals("aaaa", question.solution("aaaa"))
+        assertEquals("ynsdeit", question.solution("ynitsed"))
+        assertEquals("nuash", question.solution("nuahs"))
+        assertEquals("abdc", question.solution("abcd"))
+        assertEquals("abcd", question.solution("dcba"))
+    }
+}