Create N-Queens.cpp

N-Queens.cpp

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+#define N 4
+#include <stdbool.h>
+#include <stdio.h>
+void printSolution(int board[N][N])
+{
+    for (int i = 0; i < N; i++) {
+        for (int j = 0; j < N; j++)
+            printf(" %d ", board[i][j]);
+        printf("\n");
+    }
+}
+bool isSafe(int board[N][N], int row, int col)
+{
+    int i, j;
+    for (i = 0; i < col; i++)
+        if (board[row][i])
+            return false;
+    for (i = row, j = col; i >= 0 && j >= 0; i--, j--)
+        if (board[i][j])
+            return false;
+    for (i = row, j = col; j >= 0 && i < N; i++, j--)
+        if (board[i][j])
+            return false;
+
+    return true;
+}
+bool solveNQUtil(int board[N][N], int col)
+{
+    /* base case: If all queens are placed
+      then return true */
+    if (col >= N)
+        return true;
+
+    /* Consider this column and try placing
+       this queen in all rows one by one */
+    for (int i = 0; i < N; i++) {
+        /* Check if the queen can be placed on
+          board[i][col] */
+        if (isSafe(board, i, col)) {
+            /* Place this queen in board[i][col] */
+            board[i][col] = 1;
+
+            /* recur to place rest of the queens */
+            if (solveNQUtil(board, col + 1))
+                return true;
+
+            /* If placing queen in board[i][col]
+               doesn't lead to a solution, then
+               remove queen from board[i][col] */
+            board[i][col] = 0; // BACKTRACK
+        }
+    }
+
+    /* If the queen cannot be placed in any row in
+        this colum col  then return false */
+    return false;
+}
+
+bool solveNQ()
+{
+    int board[N][N] = { { 0, 0, 0, 0 },
+                        { 0, 0, 0, 0 },
+                        { 0, 0, 0, 0 },
+                        { 0, 0, 0, 0 } };
+
+    if (solveNQUtil(board, 0) == false) {
+        printf("Solution does not exist");
+        return false;
+    }
+
+    printSolution(board);
+    return true;
+}
+
+int main()
+{
+    solveNQ();
+    return 0;
+}