Add problem 51 - N Queens

Author: anirudhology

problems/backtracking/n_queens.go

@@ -0,0 +1,53 @@
+package backtracking
+
+func SolveNQueens(n int) [][]string {
+	// List to store combinations
+	var combinations [][]string
+	// Special case
+	if n == 0 {
+		return combinations
+	}
+	board := make([][]rune, n)
+	for i := range board {
+		board[i] = make([]rune, n)
+		for j := range board[i] {
+			board[i][j] = '.'
+		}
+	}
+	// Perform backtracking
+	backtrackForNQueens(board, 0, &combinations)
+	return combinations
+}
+
+func backtrackForNQueens(board [][]rune, index int, combinations *[][]string) {
+	if index == len(board) {
+		*combinations = append(*combinations, build(board))
+		return
+	}
+	for i := 0; i < len(board); i++ {
+		if check(board, i, index) {
+			board[i][index] = 'Q'
+			backtrackForNQueens(board, index+1, combinations)
+			board[i][index] = '.'
+		}
+	}
+}
+
+func check(board [][]rune, row, column int) bool {
+	for i := 0; i < len(board); i++ {
+		for j := 0; j < column; j++ {
+			if board[i][j] == 'Q' && (row+j == column+i || row+column == i+j || row == i) {
+				return false
+			}
+		}
+	}
+	return true
+}
+
+func build(board [][]rune) []string {
+	var combination []string
+	for _, row := range board {
+		combination = append(combination, string(row))
+	}
+	return combination
+}

tests/backtracking/n_queens_test.go

@@ -0,0 +1,52 @@
+package backtracking_test
+
+import (
+	"reflect"
+	"testing"
+
+	"github.com/anirudhology/leetcode-go/problems/backtracking"
+)
+
+func TestSolveNQueens(t *testing.T) {
+	normalize := func(input [][]string) [][]string {
+		if input == nil {
+			return [][]string{}
+		}
+		return input
+	}
+
+	result1 := backtracking.SolveNQueens(4)
+	expected1 := [][]string{
+		{"..Q.", "Q...", "...Q", ".Q.."},
+		{".Q..", "...Q", "Q...", "..Q."},
+	}
+	if !reflect.DeepEqual(normalize(result1), normalize(expected1)) {
+		t.Errorf("Expected %v but got %v", expected1, result1)
+	}
+
+	result2 := backtracking.SolveNQueens(1)
+	expected2 := [][]string{
+		{"Q"},
+	}
+	if !reflect.DeepEqual(normalize(result2), normalize(expected2)) {
+		t.Errorf("Expected %v but got %v", expected2, result2)
+	}
+
+	result3 := backtracking.SolveNQueens(0)
+	expected3 := [][]string{}
+	if !reflect.DeepEqual(normalize(result3), normalize(expected3)) {
+		t.Errorf("Expected %v but got %v", expected3, result3)
+	}
+
+	result4 := backtracking.SolveNQueens(2)
+	expected4 := [][]string{}
+	if !reflect.DeepEqual(normalize(result4), normalize(expected4)) {
+		t.Errorf("Expected %v but got %v", expected4, result4)
+	}
+
+	result5 := backtracking.SolveNQueens(3)
+	expected5 := [][]string{}
+	if !reflect.DeepEqual(normalize(result5), normalize(expected5)) {
+		t.Errorf("Expected %v but got %v", expected5, result5)
+	}
+}