C: pythagorean-triplet and saddle-point

c/saddle-points/src/saddle_points.c

@@ -0,0 +1,142 @@
+#include <stdbool.h>
+
+#include "saddle_points.h"
+
+#define POOL_SIZE 10
+#define MAX_STACK 1024
+
+static saddle_point_t stack[MAX_STACK];
+static int stack_pos;
+
+static int push_maybe(uint8_t max, uint8_t val, uint8_t r, uint8_t c)
+{
+    if (val > max) {                              /* new max value */
+        max = val;
+        stack_pos = 0;
+    }
+    if (val == max) {
+        if (stack_pos == MAX_STACK)               /* stack overflow */
+            return -1;
+        stack[stack_pos] = (saddle_point_t) {r, c};
+        stack_pos++;
+    }
+    return max;
+}
+
+static saddle_point_t *pop()
+{
+    if (!stack_pos)
+        return NULL;
+    stack_pos--;
+    return &stack[stack_pos];
+}
+
+static saddle_points_t *new_saddle_points()
+{
+    saddle_points_t *t = malloc(sizeof(saddle_points_t));
+    if (t) {
+        t->count  = 0;
+        t->pool   = 0;
+        t->points = NULL;
+    }
+    return t;
+}
+
+static saddle_points_t *add_point(saddle_points_t *saddle, const uint8_t r,
+                                  const uint8_t c)
+{
+    /* we may directly call add_point() without new_saddle_points().
+     * Not used here, but could be useful if triplets_with_sum() should
+     * return NULL when no solution found, instead of empty set.
+     */
+    if (! (saddle || (saddle = new_saddle_points())))
+        return NULL;
+
+    if (saddle->count == saddle->pool) {
+        saddle->pool += POOL_SIZE;
+        if (!(saddle->points = realloc(saddle->points, sizeof(saddle) +
+                                  saddle->pool * sizeof(saddle_point_t)))) {
+            free(saddle);
+            return NULL;
+        }
+    }
+    saddle->points[saddle->count++] = (saddle_point_t) {r, c};
+    return saddle;
+}
+
+saddle_points_t *saddle_points(uint8_t ro, uint8_t co, uint8_t m[ro][co])
+{
+    saddle_points_t *saddle;
+    saddle_point_t *possible;
+
+    if (!(saddle = new_saddle_points()))
+        return NULL;
+    /* find largest value in each row */
+    for (int16_t row = 0; row < ro; ++row) {
+        int max = 0;
+        for (int16_t col = 0; col < co; ++col) {
+            /* partial result (stack overflow) */
+            if ((max = push_maybe(max, m[row][col], row, col)) < 0)
+                return saddle;
+        }
+        /* we have now the largest row values on stack, we check if they are
+         * saddle points (= lowest in their columns)
+         */
+        while ((possible = pop())) {
+            for (int r1 = 0; r1 < ro; ++r1) {
+                if (m[possible->row][possible->column] > m[r1][possible->column])
+                    goto not_saddle;
+            }
+            saddle = add_point(saddle, possible->row+1, possible->column+1);
+        not_saddle: ;
+        }
+    }
+    return saddle;
+}
+
+void free_saddle_points(saddle_points_t *s)
+{
+    free(s->points);
+    free(s);
+}
+
+/* See GNUmakefile below for explanation
+ * https://github.com/braoult/exercism/blob/master/c/templates/GNUmakefile
+ */
+#ifdef UNIT_TEST
+#include <stdio.h>
+
+int main(int ac, char **av)
+{
+    int arg;
+    uint8_t row, col;
+    saddle_points_t *s;
+
+    if (ac > 3) {
+        row=atoi(av[1]);
+        col=atoi(av[2]);
+        arg=3;
+        if ((ac-3) == row*col) {
+            uint8_t array[row][col];
+            uint8_t *p=(uint8_t *)array;
+            printf("row=%d col=%d ac=%d arg=%d\n", row, col, ac, arg);
+            while (arg<ac)
+                *p++=atoi(av[arg++]);
+
+            for (int r=0; r<row; ++r) {
+                for (int c=0; c<col; ++c) {
+                    printf("%d ", array[r][c]);
+                }
+                printf("\n");
+            }
+            s = saddle_points(row, col, array);
+            printf("saddles: %lu\n", s->count);
+            for (unsigned i=0; i<s->count; ++i) {
+                printf("%u: (%u, %u)\n", i, s->points[i].column,
+                       s->points[i].row);
+
+            }
+        }
+    }
+}
+#endif

c/saddle-points/src/saddle_points.h

@@ -0,0 +1,36 @@
+#ifndef SADDLE_POINTS_H
+#define SADDLE_POINTS_H
+
+#include <stdint.h>
+#include <stdlib.h>
+
+typedef struct {
+    uint8_t row;
+    uint8_t column;
+} saddle_point_t;
+
+typedef struct {
+    size_t count;
+    size_t pool;
+    saddle_point_t *points;
+} saddle_points_t;
+
+extern saddle_points_t *saddle_points(uint8_t rows, uint8_t columns,
+                                      uint8_t matrix[rows][columns]);
+
+extern void free_saddle_points(saddle_points_t *saddle_point);
+
+/* See GNUmakefile below for explanation
+ * https://github.com/braoult/exercism/blob/master/c/templates/GNUmakefile
+ */
+#if defined UNIT_TEST || defined DEBUG
+#include <stdio.h>
+#include <stdlib.h>
+#endif
+
+#ifdef  TESTALL
+#undef  TEST_IGNORE
+#define TEST_IGNORE() {}
+#endif
+
+#endif