kt: add «1092. Shortest Common Supersequence»

URL:	https://leetcode.com/problems/shortest-common-supersequence/

kt/shortest-common-supersequence.kt

@@ -0,0 +1,57 @@
+class Solution {
+    fun shortestCommonSupersequence(
+        str1: String,
+        str2: String,
+    ): String {
+        val (n, m) = str1.length to str2.length
+        val dp = Array(n + 1) { IntArray(m + 1) }
+
+        // Initialize base cases
+        (0..n).forEach { y -> dp[y][0] = y }
+        (0..m).forEach { x -> dp[0][x] = x }
+
+        // Precompute
+        (1..n).flatMap { y ->
+            (1..m).map { x -> x to y }
+        }.forEach { (x, y) ->
+            dp[y][x] =
+                when {
+                    str1[y - 1] == str2[x - 1] -> dp[y - 1][x - 1] + 1
+                    else -> 1 + listOf(dp[y - 1][x], dp[y][x - 1]).min()!!
+                }
+        }
+
+        val supersequence = StringBuilder()
+        var (x, y) = m to n
+
+        while (y > 0 && x > 0) {
+            when {
+                str1[y - 1] == str2[x - 1] -> {
+                    supersequence.append(str1[y - 1])
+                    y--
+                    x--
+                }
+                dp[y - 1][x] < dp[y][x - 1] -> {
+                    supersequence.append(str1[y - 1])
+                    y--
+                }
+                else -> {
+                    supersequence.append(str2[x - 1])
+                    x--
+                }
+            }
+        }
+
+        while (y > 0) {
+            supersequence.append(str1[y - 1])
+            y--
+        }
+
+        while (x > 0) {
+            supersequence.append(str2[x - 1])
+            x--
+        }
+
+        return supersequence.reverse().toString()
+    }
+}