-
Notifications
You must be signed in to change notification settings - Fork 13
/
Backtracking_NQueenProblem.java
86 lines (76 loc) · 2.83 KB
/
Backtracking_NQueenProblem.java
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
// https://practice.geeksforgeeks.org/problems/n-queen-problem/0
// https://www.youtube.com/watch?v=0DeznFqrgAI (Best video explanation)
// https://www.geeksforgeeks.org/printing-solutions-n-queen-problem/
// https://www.geeksforgeeks.org/n-queen-problem-backtracking-3/
// https://www.youtube.com/watch?v=xFv_Hl4B83A
// https://www.youtube.com/watch?v=xouin83ebxE
public class Backtracking_NQueenProblem {
private static int N = 0;
private static StringBuilder output = new StringBuilder();
private static StringBuilder printTheBoard = new StringBuilder();
public static void main(String[] args) throws IOException {
BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
int t = Integer.parseInt(br.readLine().trim());
while (t -- > 0) {
N = Integer.parseInt(br.readLine().trim());
solveNQ();
System.out.println((output.length() == 0) ? -1 : output);
output.setLength(0);
System.out.println(printTheBoard);
printTheBoard.setLength(0);
}
}
private static void solveNQ() {
int[][] board = new int[N][N];
solveNQUtil(board, 0);
}
private static void solveNQUtil(int[][] board, int col) {
if(col >= N) {
printOutput(board);
return;
}
for (int row = 0; row < N; row++) {
if(isSafe(board, row, col)) {
board[row][col] = 1;
solveNQUtil(board, col+1);
board[row][col] = 0;
}
}
}
private static boolean isSafe(int[][] board, int row, int col) {
// check left side of that row
for (int j = 0; j < col; j++) {
if(board[row][j] == 1) return false;
}
// check left upper diagonal
for (int i = row, j = col; i >= 0 && j >= 0; i--, j--) {
if(board[i][j] == 1) return false;
}
// check left lower diagonal
for (int i = row, j = col; i < N && j >= 0; i++, j--) {
if(board[i][j] == 1) return false;
}
return true;
}
private static void printOutput(int[][] board) {
// below code prints the whole board
for (int row = 0; row < N; row++) {
for (int col = 0; col < N; col++) {
printTheBoard.append(board[row][col]);
}
printTheBoard.append("\n");
}
printTheBoard.append("\n");
// below code only prints the row col number of the board
output.append("[");
for (int col = 0; col < N; col++) {
for (int row = 0; row < N; row++) {
if(board[row][col] == 1) output.append(row+1).append(" ");
}
}
output.append("] ");
}
}