word search solution

Author: yhkee0404

word-search/yhkee0404.kt

@@ -0,0 +1,58 @@
+val _DRCS = listOf(
+    listOf(0, -1),
+    listOf(0, 1),
+    listOf(-1, 0),
+    listOf(1, 0),
+)
+
+class Solution {
+    fun exist(board: Array<CharArray>, word: String): Boolean {
+        val offset = 'A'.code
+        val invertedIndex = List('z'.code - offset + 1) {mutableListOf<List<Int>>()}
+        board.withIndex()
+                .forEach { row ->
+                    row.value
+                            .withIndex()
+                            .forEach {
+                                invertedIndex[it.value.toInt() - offset].add(listOf(row.index, it.index))
+                            }
+                }
+        val freq = MutableList(invertedIndex.size) {0}
+        word.map {it.toInt() - offset}
+                .forEach {
+                    freq[it]++
+                }
+        if ((0 until freq.size).any {freq[it] > invertedIndex[it].size}) {
+            return false
+        }
+        val target = if (invertedIndex[word.first().toInt() - offset].size <= invertedIndex[word.last().toInt() - offset].size) word
+        else word.reversed()
+        val stack = invertedIndex[target.first().toInt() - offset].map {
+                    mutableListOf(it.first(), it.last(), 0, 1)
+                }.toMutableList()
+        val visited = MutableList(board.size) {MutableList(board.first().size) {false}}
+        while (! stack.isEmpty()) {
+            val u = stack.last()
+            if (u[2] == 4) {
+                visited[u[0]][u[1]] = false
+                stack.removeLast()
+                continue
+            }
+            if (u[2] == 0) {
+                if (u[3] == target.length) {
+                    return true
+                }
+                visited[u[0]][u[1]] = true
+            }
+            val drc = _DRCS[u[2]]
+            u[2]++
+            val v = mutableListOf(u[0] + drc[0], u[1] + drc[1], 0, u[3] + 1)
+            if (v[0] == -1 || v[0] == board.size || v[1] == -1 || v[1] == board.first().size
+                    || visited[v[0]][v[1]] || board[v[0]][v[1]] != target[u[3]]) {
+                continue
+            }
+            stack.add(v)
+        }
+        return false
+    }
+}