Adding jarvis march in c (#91)

Author: Gathros

chapters/computational_geometry/gift_wrapping/jarvis_march/code/c/jarvis_march.c

@@ -0,0 +1,70 @@
+#include <stdio.h>
+#include <stddef.h>
+#include <stdbool.h>
+
+struct point {
+ double x,y;
+};
+
+struct point left_most_point(struct point *points, size_t num_points) {
+ struct point ret = points[0];
+
+ for (size_t i = 0; i < num_points; ++i) {
+ if (points[i].x < ret.x) {
+ ret = points[i];
+ } else if(points[i].x == ret.x) {
+ if (points[i].y < ret.y) {
+ ret = points[i];
+ }
+ }
+ }
+
+ return ret;
+}
+
+bool equal(struct point a, struct point b) {
+ return a.x == b.x && a.y == b.y;
+}
+
+double winding(struct point p, struct point q, struct point r) {
+ return (q.x - p.x)*(r.y - p.y) - (q.y - p.y)*(r.x - p.x);
+}
+
+size_t jarvis_march(struct point *points, struct point *hull_points,
+ size_t num_points) {
+ struct point hull_point = left_most_point(points, num_points);
+ struct point end_point;
+
+ size_t i = 0;
+ do {
+ hull_points[i] = hull_point;
+ end_point = points[0];
+
+ for (size_t j = 1; j < num_points; ++j) {
+ if (equal(end_point, hull_point) ||
+ winding(hull_points[i], end_point, points[j]) > 0.0) {
+ end_point = points[j];
+ }
+ }
+
+ i++;
+ hull_point = end_point;
+ } while (!equal(end_point, hull_points[0]));
+
+ return i;
+}
+
+int main() {
+ struct point points[] = {{0.0, 0.0}, {-1.0, -1.0}, {1.0, 1.0}, {0.0, 1.0},
+ {0.0, -1.0}, {2.0, 2.0}};
+ struct point hull_points[6];
+
+ size_t num_hull_points = jarvis_march(points, hull_points, 6);
+
+ printf("The Hull points are:\n");
+ for (size_t i = 0; i < num_hull_points; ++i) {
+ printf("x=%f y=%f\n", hull_points[i].x, hull_points[i].y);
+ }
+
+ return 0;
+}