C solution for week 88, part 2.

1 files changed, 151 insertions, 0 deletions

diff --git a/challenge-088/abigail/c/ch-2.c b/challenge-088/abigail/c/ch-2.c
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+# include <stdlib.h>
+# include <stdio.h>
+
+/*
+ * Challenge
+ *
+ * You are given m x n matrix of positive integers.
+ * 
+ * Write a script to print spiral matrix as list.
+ */ 
+
+/*
+ * We solve this by keeping track of the boundaries (min_x, min_y, max_x,
+ * max_y) of the part of the matrix which still needs to be processed.
+ * Initially, min_x and min_y are 0, max_x is the index of the bottom row,
+ * and max_y is the index of the right most column.
+ *
+ * We then process the matrix side by side, first going east (top row), 
+ * south (left column), west (bottom row), then north (left row). After
+ * doing a side, we update the corresponding min/max value. That is,
+ * after doing the top row, we increment min_x; right column, decrement
+ * max_y; bottom row, decrement max_x; left column, increment min_y.
+ *
+ * We're done when min_x > max_x, or min_y > max_y.
+ */
+
+typedef long long  number;
+enum    dirs      {EAST, SOUTH, WEST, NORTH};
+
+int main (void) {
+    char *     text     = NULL; /* Complete input                     */
+    size_t     buf_len  = 0;    /* Allocated buffer size              */
+    ssize_t    str_len;         /* Number of characters read          */
+    size_t     rows     = 0;    /* Number of rows in matrix           */
+    size_t     columns  = 0;    /* Number of columns in matrix        */
+    size_t     elements = 0;    /* Total number of elemenst in matrix */
+
+    number     element;         /* Element read                       */
+    int        offset;          /* Offset when scanning input         */
+    char *     ptr;             /* Pointer into text                  */
+    number **  matrix;          /* Matrix we're using                 */
+
+    enum dirs  direction;       /* Direction of movement              */
+
+
+    /* Read all the input (this assumes the input doesn't contain  *
+     * a NUL character.                                            */
+    str_len = getdelim (&text, &buf_len, 0, stdin);
+
+    /* First, count the number of rows */
+    ptr = text;
+    while (*ptr) {
+        if (*ptr == '\n') {
+            rows ++;
+        }
+        ptr ++;
+    }
+
+    /* Count the number of elements */
+    ptr = text;
+    while (sscanf (ptr, "%lld%n", &element, &offset) == 1) {
+        elements ++;
+        ptr += offset;
+    }
+
+    /* We can now calculate the number of columns */
+    columns = elements / rows;
+
+    /* Check whether we have any elements left over; *
+     * if so, we exit with an error.                 */
+    if (elements != rows * columns) {
+        fprintf (stderr, "That doesn't look like a proper matrix\n");
+        exit (1);
+    }
+
+    /* Allocate memory */
+    if ((matrix = (number **) calloc (rows, sizeof (number *))) == NULL) {
+        fprintf (stderr, "Out of memory\n");
+        exit (1);
+    }
+
+    for (size_t x = 0; x < rows; x ++) {
+        if ((matrix [x] = (number *) calloc (columns,
+                                             sizeof (number))) == NULL) {
+            fprintf (stderr, "Out of memory\n");
+            exit (1);
+        }
+    }
+
+    /* Scan the text again, but now fill in the array */
+    ptr = text;
+    for (int x = 0; x < rows; x ++) {
+        for (int y = 0; y < columns; y ++) {
+            if (sscanf (ptr, "%lld%n", &matrix [x] [y], &offset) != 1) {
+                fprintf (stderr, "Something really weird happened!\n");
+                exit (1);
+            }
+            ptr += offset;
+        }
+    }
+
+    /* Now it's time to do the real work */
+    /* Note that we're using ssize_t for the min/max values; if we use  *
+     * unsigned values, we're running into problems if we use a loop    *
+     * counting down to zero. We would expect the loop to terminate if  *
+     * the iterand is -1, but that cannot happen for an unsigned value. */
+    ssize_t min_x = 0;
+    ssize_t max_x = rows    - 1;
+    ssize_t min_y = 0;
+    ssize_t max_y = columns - 1;
+
+    direction = EAST;   /* We start off heading East */
+
+    size_t printed = 0; /* Each printed number will be preceeded by a  *
+                         * comma, except the first.                    */
+    while (min_x <= max_x && min_y <= max_y) {
+        if (direction == EAST) {
+            for (ssize_t y = min_y; y <= max_y; y ++) {
+                printf (printed ++ ? ", %lld" : "%lld", matrix [min_x] [y]);
+            }
+            min_x ++;
+        }
+        if (direction == SOUTH) {
+            for (ssize_t x = min_x; x <= max_x; x ++) {
+                printf (", %lld", matrix [x] [max_y]);
+            }
+            max_y --;
+        }
+        if (direction == WEST) {
+            for (ssize_t y = max_y; y >= min_y; y --) {
+                printf (", %lld", matrix [max_x] [y]);
+            }
+            max_x --;
+        }
+        if (direction == NORTH) {
+            for (ssize_t x = max_x; x >= min_x; x --) {
+                printf (", %lld", matrix [x] [min_y]);
+            }
+            min_y ++;
+        }
+        direction = (direction + 1) % (NORTH + 1);
+    }
+    printf ("\n");
+       
+    /* Clean up the allocated memory */
+    for (size_t x = 0; x < rows; x ++) {
+        free (matrix [x]);
+    }
+    free (matrix);
+    free (text);
+}