add kotlin solution for 752 - Open the Lock

kotlin/0752-open-the-lock.kt

@@ -0,0 +1,47 @@
+class Solution {
+
+    fun openLock(deadends: Array<String>, target: String): Int {
+        val deadEndSet = hashSetOf<String>()
+        deadends.forEach { deadEndSet.add(it) }
+        if (target in deadEndSet || "0000" in deadEndSet) return -1
+        // [ (String,Level) ]
+        val queue: Queue<Pair<String, Int>> = LinkedList<Pair<String, Int>>().apply {
+            add(Pair("0000", 0))
+        }
+        val visitedCombinations = hashSetOf<String>()
+
+        while (queue.isNotEmpty()) {
+            val (currentCombination, levelOfCurrentCombination) = queue.remove()
+            if (currentCombination == target) return levelOfCurrentCombination
+            // increments
+            for (i in currentCombination.indices) {
+                val digitAtIndex = Character.digit(currentCombination[i], 10)
+                val incrementedValue = Character.forDigit((digitAtIndex + 1) % 10, 10)
+                val newCombination = currentCombination.replaceCharAt(i, incrementedValue)
+                if (newCombination in visitedCombinations || newCombination in deadEndSet) continue
+                visitedCombinations.add(newCombination)
+                queue.add(Pair(newCombination, levelOfCurrentCombination + 1))
+            }
+            // decrements
+            for (i in currentCombination.indices) {
+                val valueAtIndex = Character.digit(currentCombination[i], 10)
+                val decrementedValue = Character.forDigit(
+                    (valueAtIndex - 1).takeIf { valueAtIndex - 1 in 0..9 } ?: 9, 10)
+                val newCombination = currentCombination.replaceCharAt(i, decrementedValue)
+                if (newCombination in visitedCombinations || newCombination in deadEndSet) continue
+                visitedCombinations.add(newCombination)
+                queue.add(Pair(newCombination, levelOfCurrentCombination + 1))
+            }
+        }
+        return -1
+    }
+
+    private fun String.replaceCharAt(
+        index: Int,
+        newChar: Char
+    ): String = when (index) {
+        0 -> newChar + substring(1..this.lastIndex)
+        lastIndex -> substring(0 until this.lastIndex) + newChar
+        else -> substring(0 until index) + newChar + substring(index + 1..this.lastIndex)
+    }
+}