Add Verify Sudoku Board

Author: marttp

kotlin/Hash Maps and Sets/VerifySudokuBoard.kt

@@ -0,0 +1,41 @@
+fun verifySudokuBoard(board: List<List<Int>>): Boolean {
+    // Create hash sets for each row, column, and subgrid to keep
+    // track of numbers previously seen on any given row, column, or
+    // subgrid.
+    val rowSets: List<HashSet<Int>> = List(9) {
+        hashSetOf()
+    }
+    val colSets: List<HashSet<Int>> = List(9) {
+        hashSetOf()
+    }
+    val subgridSets: List<List<HashSet<Int>>> = List(3) {
+        List(3) {
+            hashSetOf()
+        }
+    }
+    for (r in 0 until 9) {
+        for (c in 0 until 9) {
+            val num = board[r][c]
+            if (num == 0) {
+                continue
+            }
+            // Check if 'num' has been seen in the current row,
+            // column, or subgrid.
+            if (rowSets[r].contains(num)) {
+                return false
+            }
+            if (colSets[c].contains(num)) {
+                return false
+            }
+            if (subgridSets[r / 3][c / 3].contains(num)) {
+                return false
+            }
+            // If we passed the above checks, mark this value as seen 
+            // by adding it to its corresponding hash sets.
+            rowSets[r].add(num)
+            colSets[c].add(num)
+            subgridSets[r / 3][c / 3].add(num)
+        }
+    }
+    return true
+}