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2013-07-05T08:49:58.190
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My idea is that a 2D array can (in some cases) be considered as a 1D array because of the memory storage of it. If not, you can either copy it into a 1D array of write a custom sort function that use a function that translate the indexes from 1D to 2D. Here an example using the function qsort: <pre><code>#include <stdio.h> #include <stdlib.h> int matrix[4][4]; void print_matrix() { int i, j; for (i = 0; i < 4; i++) { for (j = 0; j < 4; j++) { printf("%d ", matrix[i][j]); } printf("\n"); } } int compar(const void *a, const void *b) { int ia = *((int*)a); int ib = *((int*)b); return ia - ib; } int main() { int i, j; // Init of a 2D array with random numbers: for (i = 0; i < 4; i++) { for (j = 0; j < 4; j++) { matrix[i][j] = random() % 10; } } // Before: printf("Before:\n"); print_matrix(); // This array can be considered as a big 1D array. qsort(matrix, 16, sizeof(int), compar); // After: printf("After:\n"); print_matrix(); return 0; } </code></pre> Output: <pre><code>Before: 3 6 7 5 3 5 6 2 9 1 2 7 0 9 3 6 After: 0 1 2 2 3 3 3 5 5 6 6 6 7 7 9 9 </code></pre> Edit: OP asked me to avoid using qsort... So here a quicksort able to sort a 2D array: <pre><code>#include <stdio.h> #include <stdlib.h> void print_matrix(int **matrix, int rows, int cols) { int i, j; for (i = 0; i < rows; i++) { for (j = 0; j < cols; j++) { printf("%d ", matrix[i][j]); } printf("\n"); } } void swap(int *a, int *b) { int buf = *a; *a = *b; *b = buf; } int partition(int **a, int l, int r, int c) { int i; // Left pivot int pivot_val = a[l/c][l%c]; // Move pivot to end swap(&a[l/c][l%c], &a[r/c][r%c]); // If <= to the pivot value, swap int j = l; for (i = l; i < r; i++) { if (a[i/c][i%c] <= pivot_val) { swap(&a[i/c][i%c], &a[j/c][j%c]); j++; } } // Move pivot to its place. swap(&a[j/c][j%c], &a[r/c][r%c]); return j; } void quicksort_r(int **a, int l, int r, int c) { if (l < r) { int pivot = partition(a, l, r, c); quicksort_r(a, l, pivot-1, c); quicksort_r(a, pivot+1, r, c); } } void quicksort(int **a, int rows, int cols) { quicksort_r(a, 0, rows * cols - 1, cols); } int main() { int i, j; int rows = 5; int cols = 4; int **matrix = malloc(sizeof(int*) * rows); // Init of a 2D array with random numbers: for (i = 0; i < rows; i++) { matrix[i] = malloc(sizeof(int) * cols); for (j = 0; j < cols; j++) { matrix[i][j] = random() % 10; } } // Before: printf("Before:\n"); print_matrix(matrix, rows, cols); quicksort(matrix, rows, cols); // After: printf("After:\n"); print_matrix(matrix, rows, cols); return 0; } </code></pre> Which gives: <pre><code>Before: 3 6 7 5 3 5 6 2 9 1 2 7 0 9 3 6 0 6 2 6 After: 0 0 1 2 2 2 3 3 3 5 5 6 6 6 6 6 7 7 9 9 </code></pre> Edit2: I realized afterward that there is another obvious solution for square matrices: Let's take the first example: <pre><code>0 1 2 2 3 3 3 5 5 6 6 6 7 7 9 9 </code></pre> There is also: <pre><code>0 3 5 7 1 3 6 7 2 3 6 9 2 5 6 9 </code></pre> But for the second example too: <pre><code>0 0 1 2 2 2 3 3 3 5 5 6 6 6 6 6 7 7 9 9 </code></pre> And: <pre><code>0 2 3 6 0 2 5 6 1 3 5 6 2 3 6 6 7 7 9 9 </code></pre> Which means that maybe we could do a specialized algorithm able to give all the solutions or an algorithm that tries to minimize the number of moves, I don't know. It's a quite interesting problem in fact.
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1. POHow to sort a 2D Matrix
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1. USMaxime Chéramy
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1. USMaxime Chéramy
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