added n-queen solution

n-queen.c

@@ -0,0 +1,108 @@
+#include <stdio.h>
+#include <stdlib.h>
+
+void queen(int k) {
+    switch (k) {
+    case 1: printf("|      **      |"); break;
+    case 2: printf("|    ******    |"); break;
+    case 3: printf("|    ******    |"); break;
+    case 4: printf("|      **      |"); break;
+    case 5: printf("|      **      |"); break;
+    case 6: printf("|      **      |"); break;
+    case 7: printf("|   ********   |"); break;
+    case 8: printf("|**************|"); break;
+    }
+}
+
+void blank() {
+    printf("|              |");
+}
+
+int is_safe(int** arr, int x, int y, int n) {
+    for (int row = 0; row < x; row++) {
+        if (arr[row][y] == 1) {
+            return 0;
+        }
+    }
+
+    int row = x;
+    int col = y;
+
+    // left diagonal
+    while (row >= 0 && col >= 0) {
+        if (arr[row][col] == 1) {
+            return 0;
+        }
+        row--;
+        col--;
+    }
+
+    row = x;
+    col = y;
+
+    // right diagonal
+    while (row >= 0 && col < n) {
+        if (arr[row][col] == 1) {
+            return 0;
+        }
+        row--;
+        col++;
+    }
+    return 1;
+}
+
+int nQueen(int** arr, int x, int n) {
+    if (x >= n) {
+        return 1;
+    }
+
+    for (int col = 0; col < n; col++) {
+        if (is_safe(arr, x, col, n)) {
+            arr[x][col] = 1;
+
+            if (nQueen(arr, x + 1, n)) {
+                return 1;
+            }
+            arr[x][col] = 0; // backtrack
+        }
+    }
+    return 0;
+}
+
+int main() {
+    printf("Enter the size:\n");
+    int n;
+    scanf("%d", &n);
+
+    int** arr = (int**)malloc(sizeof(int*) * n);
+    for (int i = 0; i < n; i++) {
+        arr[i] = (int*)malloc(sizeof(int) * n);
+        for (int j = 0; j < n; j++) {
+            arr[i][j] = 0;
+        }
+    }
+
+    if (nQueen(arr, 0, n)) {
+        for (int i = 0; i < n; i++) {
+            int f = 1;
+            for (int k = 1; k <= 8; k++) {
+                for (int j = 0; j < n; j++) {
+                    if (arr[i][j] == 1) {
+                        queen(k);
+                    } else {
+                        blank();
+                    }
+                }
+                printf("\n");
+            }
+            printf("\n");
+        }
+    }
+
+    for (int i = 0; i < n; i++) {
+        free(arr[i]);
+    }
+    free(arr);
+
+    return 0;
+}