Merge pull request hacktoberfest17#470 from felipecustodio/felipecustodio_nqueens_c

N-Queens problem in C

Author: t2013anurag

nqueens/nqueens.c

@@ -0,0 +1,162 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <time.h>
+
+#define bool char
+#define TRUE 1
+#define FALSE 0
+
+typedef struct board {
+    int n;
+    int** matrix;
+} BOARD;
+
+void printStep(BOARD* b, int x, int y) {
+    int i, j;
+    for (i = 0; i < b->n; i++) {
+        for (j = 0; j < b->n; j++) {
+            if (i == x && j == y) {
+                printf(" ");
+            } else {
+                if (b->matrix[i][j]) {
+                    printf(" ");
+                } else {
+                    printf(" ");
+                }
+            }
+        }
+        printf("\n");
+    }
+    printf("\n\n");
+}
+
+bool isValid(BOARD* b, int x, int y) {
+
+    int i, j;
+    // check horizontal
+    for (i = 0; i < b->n; i++) {
+        if (i != y && b->matrix[x][i] == 1) return FALSE;
+    }
+
+    // check vertical
+    for (i = 0; i < b->n; i++) {
+        if (i != x && b->matrix[i][y] == 1) return FALSE;
+    }
+    // check diagonals
+    // check top left
+    i = x;
+    j = y;
+    while (i >= 0 && j >= 0) {
+        if (i != x && j != y && b->matrix[i][j] == 1) {
+            return FALSE;
+        }
+        i--;
+        j--;
+    }
+    // check top right
+    i = x;
+    j = y;
+    while (i >= 0 && j < b->n) {
+        if (i != x && j != y && b->matrix[i][j] == 1) {
+            return FALSE;
+        }
+        i--;
+        j++;
+    }
+    // check bottom left
+    i = x;
+    j = y;
+    while (i < b->n && j >= 0) {
+        if (i != x && j != y && b->matrix[i][j] == 1) {
+            return FALSE;
+        }
+        i++;
+        j--;
+    }
+    // check bottom right
+    i = x;
+    j = y;
+    while (i < b->n && j < b->n) {
+        if (i != x && j != y && b->matrix[i][j] == 1) {
+            return FALSE;
+        }
+        i++;
+        j++;
+    }
+    return TRUE;
+}
+
+bool placeQueen(BOARD** b, int line, long int* calls) {
+    int i;
+    if (line >= (*b)->n) return TRUE;
+    for (i = 0; i < (*b)->n; i++) {
+        (*b)->matrix[line][i] = 1;
+        (*calls)++;
+        if (isValid((*b), line, i) && placeQueen(b, line+1, calls)) {
+            return TRUE;
+        }
+        (*b)->matrix[line][i] = 0;
+    }
+    return FALSE;
+}
+
+void printBoard(BOARD* b) {
+    int i, j;
+    for (i = 0; i < b->n; i++) {
+        for (j = 0; j < b->n; j++) {
+            if (b->matrix[i][j]) {
+                printf(" ");
+            } else {
+                printf(" ");
+            }
+        }
+        printf("\n");
+    }
+}
+
+void queens(int n) {
+    // benchmarking
+    clock_t start_t, end_t;
+    float delta_t = 0.0;
+    long int calls = 0;
+    int i, j;
+    BOARD* b = (BOARD*)malloc(sizeof(BOARD));
+    b->n = n;
+    b->matrix = (int**)malloc(sizeof(int*) * n);
+    for (i = 0; i < n; i++) {
+        b->matrix[i] = (int*)malloc(sizeof(int) * n);
+        for (j = 0; j < n; j++) {
+            b->matrix[i][j] = 0;
+        }
+    }
+
+    start_t = clock();
+    if (placeQueen(&b, 0, &calls)) {
+        end_t = clock();
+        // human readable time
+        delta_t = ((float)(end_t - start_t) / 1000000000000.0F ) * CLOCKS_PER_SEC;
+        printBoard(b);
+        printf("%d,%ld,%lfs\n", n, calls, delta_t);
+    }
+
+    for (i = 0; i < n; i++) {
+        free(b->matrix[i]);
+        b->matrix[i] = NULL;
+    }
+    free(b->matrix);
+    b->matrix = NULL;
+    free(b);
+}
+
+int main(int argc, char const *argv[]) {
+    system("clear");
+    int i;
+    int n = 0;
+    scanf("%d", &n);
+    printf("board size,calls,time\n");
+    for (i = 0; i <= n; i++) {
+        queens(i);
+    }
+
+    return 0;
+}