Infra-intern-assessment solution

sudoku.go

@@ -1 +1,70 @@
 package main
+
+import (
+	"container/list"
+)
+
+func dfs(board *[][]int, queue *list.List, rows *[9][9]int, columns *[9][9]int, groups *[9][9]int) bool {
+	// if the length of the process queue is empty then all empty nodes
+	// have been filled without ever violating the frequency constraint
+	if queue.Len() == 0 {
+		return true // return here, the current state of the board is the solution
+	}
+
+	// grab current node for processing
+	elem := queue.Front()
+	cur := elem.Value.([]int)
+	x, y := cur[0], cur[1]
+
+	for i := 0; i < 9; i++ {
+		// iterate through 9 possible values for this node, determine if a solution exists
+		if (*rows)[y][i] == 0 && (*columns)[x][i] == 0 && (*groups)[(y/3)*3+(x/3)][i] == 0 { // check for violations
+			// add this number and remove it from the queue, then check the next node in queue
+			queue.Remove(queue.Front())
+			(*rows)[y][i] = 1
+			(*columns)[x][i] = 1
+			(*groups)[(y/3)*3+(x/3)][i] = 1
+			(*board)[y][x] = i + 1
+
+			if dfs(board, queue, rows, columns, groups) {
+				return true
+			} else {
+				// the recursive call has not found a solution, so this value cannot work, move on
+				(*rows)[y][i] = 0
+				(*columns)[x][i] = 0
+				(*groups)[(y/3)*3+(x/3)][i] = 0
+				(*board)[y][x] = 0
+				queue.PushFront([]int{x, y})
+			}
+		}
+	}
+
+	return false
+}
+
+func SolveSudoku(board [][]int) [][]int {
+	// Fill in adjacency matrices mapping which numbers are
+	// present in rows/column/groups
+
+	rows := [9][9]int{}
+	columns := [9][9]int{}
+	groups := [9][9]int{}
+	queue := list.New() // use Linked List for O(1) popping & left append
+
+	for y := 0; y < 9; y++ {
+		for x := 0; x < 9; x++ {
+			if board[y][x] == 0 { // if a node is empty, mark it for processing
+				queue.PushBack([]int{x, y})
+			} else { // else document it in our matrices
+				rows[y][board[y][x]-1] = 1
+				columns[x][board[y][x]-1] = 1
+				groups[(y/3)*3+(x/3)][board[y][x]-1] = 1
+			}
+		}
+	}
+
+	// call the dfs function to compute a solution of the board
+	dfs(&board, queue, &rows, &columns, &groups)
+
+	return board
+}