HACKTOBERFEST 2022

N-Queen(FSS)101.java

@@ -0,0 +1,89 @@
+// Way to solve the N-Queen problem 
+
+import java.util.Arrays;
+
+class Main
+{
+    // Function to check if two queens threaten each other or not
+    private static boolean isSafe(char[][] mat, int r, int c)
+    {
+        // return false if two queens share the same column
+        for (int i = 0; i < r; i++)
+        {
+            if (mat[i][c] == 'Q') {
+                return false;
+            }
+        }
+
+        // return false if two queens share the same `` diagonal
+        for (int i = r, j = c; i >= 0 && j >= 0; i--, j--)
+        {
+            if (mat[i][j] == 'Q') {
+                return false;
+            }
+        }
+
+        // return false if two queens share the same `/` diagonal
+        for (int i = r, j = c; i >= 0 && j < mat.length; i--, j++)
+        {
+            if (mat[i][j] == 'Q') {
+                return false;
+            }
+        }
+
+        return true;
+    }
+
+    private static void printSolution(char[][] mat)
+    {
+        for (char[] chars: mat) {
+            System.out.println(Arrays.toString(chars).replaceAll(",", ""));
+        }
+        System.out.println();
+    }
+
+    private static void nQueen(char[][] mat, int r)
+    {
+        // if `N` queens are placed successfully, print the solution
+        if (r == mat.length)
+        {
+            printSolution(mat);
+            return;
+        }
+
+        // place queen at every square in the current row `r`
+        // and recur for each valid movement
+        for (int i = 0; i < mat.length; i++)
+        {
+            // if no two queens threaten each other
+            if (isSafe(mat, r, i))
+            {
+                // place queen on the current square
+                mat[r][i] = 'Q';
+
+                // recur for the next row
+                nQueen(mat, r + 1);
+
+                // backtrack and remove the queen from the current square
+                mat[r][i] = '–';
+            }
+        }
+    }
+
+    public static void main(String[] args)
+    {
+        // `N × N` chessboard
+        int N = 8;
+
+        // `mat[][]` keeps track of the position of queens in
+        // the current configuration
+        char[][] mat = new char[N][N];
+
+        // initialize `mat[][]` by `-`
+        for (int i = 0; i < N; i++) {
+            Arrays.fill(mat[i], '–');
+        }
+
+        nQueen(mat, 0);
+    }
+}