Add Convex Hull in C

archive/c/c/convex-hull.c

@@ -0,0 +1,134 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <stdbool.h>
+
+typedef struct {
+    int x;
+    int y;
+} Point;
+
+int compare(const void *p1, const void *p2) {
+    Point *point1 = (Point *)p1;
+    Point *point2 = (Point *)p2;
+
+    if (point1->x != point2->x) {
+        return point1->x - point2->x;
+    }
+    return point1->y - point2->y;
+}
+
+int orientation(Point p, Point q, Point r) {
+    int val = (q.y - p.y) * (r.x - q.x) - (q.x - p.x) * (r.y - q.y);
+    return (val == 0) ? 0 : (val > 0) ? 1 : 2;
+}
+
+void convexHull(Point points[], int n) {
+    if (n < 3) return;
+
+    Point hull[n];
+
+    qsort(points, n, sizeof(Point), compare);
+
+    int l = 0;
+    for (int i = 1; i < n; i++)
+        if (points[i].x < points[l].x)
+            l = i;
+
+    int p = l, q;
+    do {
+        hull[0] = points[p];
+        q = (p + 1) % n;
+
+        for (int i = 0; i < n; i++) {
+            if (orientation(points[p], points[i], points[q]) == 2) {
+                q = i;
+            }
+        }
+
+        p = q;
+    } while (p != l);
+
+    for (int i = 0; i < n; i++) {
+        bool found = false;
+        for (int j = 0; j < n; j++) {
+            if (hull[j].x == points[i].x && hull[j].y == points[i].y) {
+                found = true;
+                break;
+            }
+        }
+        if (!found) {
+            hull[n++] = points[i];
+        }
+    }
+
+    for (int i = 0; i < n; i++) {
+        printf("(%d, %d)\n", hull[i].x, hull[i].y);
+    }
+}
+
+bool isInteger(const char *s) {
+    while (*s) {
+        if (*s < '0' || *s > '9') {
+            return false;
+        }
+        s++;
+    }
+    return true;
+}
+
+void parseCoordinates(char *inputX, char *inputY) {
+    char *tokenX = strtok(inputX, ",");
+    char *tokenY = strtok(inputY, ",");
+
+    Point *points = NULL;
+    int count = 0;
+
+    while (tokenX && tokenY) {
+        if (!isInteger(tokenX) || !isInteger(tokenY)) {
+            printf("Invalid Integers\n");
+            return;
+        }
+
+        points = realloc(points, sizeof(Point) * (count + 1));
+        points[count].x = atoi(tokenX);
+        points[count].y = atoi(tokenY);
+        count++;
+
+        tokenX = strtok(NULL, ",");
+        tokenY = strtok(NULL, ",");
+    }
+
+    if (tokenX || tokenY) {
+        printf("Different Cardinality\n");
+        free(points);
+        return;
+    }
+
+    if (count < 3) {
+        printf("Usage: please provide at least 3 x and y coordinates as separate lists (e.g. \"100, 440, 210\")\n");
+        free(points);
+        return;
+    }
+
+    convexHull(points, count);
+    free(points);
+}
+
+int main(int argc, char *argv[]) {
+    if (argc != 3) {
+        printf("Usage: please provide two coordinate lists (x, y)\n");
+        return 1;
+    }
+
+    char *inputX = argv[1];
+    char *inputY = argv[2];
+
+    if (strlen(inputY) == 0) {
+        printf("Missing Y\n");
+        return 1;
+    }
+
+    parseCoordinates(inputX, inputY);
+    return 0;
+}