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Added NQueens in Java #1531
Added NQueens in Java #1531
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/** | ||
N-Queens problem is a famous problem | ||
The paradigm used to solve the problem is backtracking | ||
The problem is to find a way to place n queens on nXn board | ||
such that no queen can kill the other | ||
**/ | ||
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import java.io.*; | ||
import java.util.*; | ||
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public class NQueens { | ||
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public static void solve(boolean[][] board, boolean[] cols, | ||
boolean[] ndiag, boolean[] rdiag, int row, String asf) { | ||
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if(row == board.length) { | ||
System.out.println(asf+'.'); | ||
return; | ||
} | ||
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for(int col=0; col<board.length; col++) { | ||
There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more. Can you put apt comments on your Code for better explainability? |
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if(cols[col] == false && ndiag[row+col] == false && | ||
rdiag[row-col+board.length-1] == false) { | ||
// place the queen | ||
There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more. Can you make the comments more understandable? |
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// let the column get occpied | ||
// correspondingly ndiag and rdiag | ||
// matrices are populated | ||
cols[col] = true; | ||
ndiag[row+col] = true; | ||
rdiag[row-col+board.length-1] = true; | ||
board[row][col] = true; | ||
solve(board, cols, ndiag, rdiag, row+1, asf+row+'-'+col+", "); | ||
// backtrack | ||
There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more. Can you make the comments more understandable? |
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// remove all the markings | ||
// made in the above step | ||
cols[col] = false; | ||
ndiag[row+col] = false; | ||
rdiag[row-col+board.length-1] = false; | ||
board[row][col] = false; | ||
} | ||
} | ||
} | ||
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public static void main(String[] args) throws Exception { | ||
Scanner scn = new Scanner(System.in); | ||
int n = scn.nextInt(); | ||
boolean[][] board = new boolean[n][n]; | ||
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boolean[] cols = new boolean[n]; | ||
boolean[] ndiag = new boolean[2*n-1]; | ||
boolean[] rdiag = new boolean[2*n-1]; | ||
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solve(board, cols, ndiag, rdiag, 0, ""); | ||
} | ||
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} | ||
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/** | ||
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Input : | ||
4 | ||
Output : | ||
0-1, 1-3, 2-0, 3-2, . | ||
0-2, 1-0, 2-3, 3-1, . | ||
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Space Complexity : O(n^2) | ||
Time Complexity : upperbounded by O(n^n) | ||
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**/ | ||
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If possible, please add further information about the Algorithm