Task: Convex hull
C: #include <assert.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
 
typedef struct tPoint {
    int x, y;
} Point;
 
bool ccw(const Point *a, const Point *b, const Point *c) {
    return (b->x - a->x) * (c->y - a->y)
         > (b->y - a->y) * (c->x - a->x);
}
 
int comparePoints(const void *lhs, const void *rhs) {
    const Point* lp = lhs;
    const Point* rp = rhs;
    if (lp->x < rp->x)
        return -1;
    if (rp->x < lp->x)
        return 1;
    if (lp->y < rp->y)
        return -1;
    if (rp->y < lp->y)
        return 1;
    return 0;
}

void fatal(const char* message) {
    fprintf(stderr, "%s\n", message);
    exit(1);
}

void* xmalloc(size_t n) {
    void* ptr = malloc(n);
    if (ptr == NULL)
        fatal("Out of memory");
    return ptr;
}

void* xrealloc(void* p, size_t n) {
    void* ptr = realloc(p, n);
    if (ptr == NULL)
        fatal("Out of memory");
    return ptr;
}

void printPoints(const Point* points, int len) {
    printf("[");
    if (len > 0) {
        const Point* ptr = points;
        const Point* end = points + len;
        printf("(%d, %d)", ptr->x, ptr->y);
        ++ptr;
        for (; ptr < end; ++ptr)
            printf(", (%d, %d)", ptr->x, ptr->y);
    }
    printf("]");
}
 
Point* convexHull(Point p[], int len, int* hsize) {
    if (len == 0) {
        *hsize = 0;
        return NULL;
    }

    int i, size = 0, capacity = 4;
    Point* hull = xmalloc(capacity * sizeof(Point));

    qsort(p, len, sizeof(Point), comparePoints);
 
    
    for (i = 0; i < len; ++i) {
        while (size >= 2 && !ccw(&hull[size - 2], &hull[size - 1], &p[i]))
            --size;
        if (size == capacity) {
            capacity *= 2;
            hull = xrealloc(hull, capacity * sizeof(Point));
        }
        assert(size >= 0 && size < capacity);
        hull[size++] = p[i];
    }
 
    
    int t = size + 1;
    for (i = len - 1; i >= 0; i--) {
        while (size >= t && !ccw(&hull[size - 2], &hull[size - 1], &p[i]))
            --size;
        if (size == capacity) {
            capacity *= 2;
            hull = xrealloc(hull, capacity * sizeof(Point));
        }
        assert(size >= 0 && size < capacity);
        hull[size++] = p[i];
    }
    --size;
    assert(size >= 0);
    hull = xrealloc(hull, size * sizeof(Point));
    *hsize = size;
    return hull;
}
 
int main() {
    Point points[] = {
        {16,  3}, {12, 17}, { 0,  6}, {-4, -6}, {16,  6},
        {16, -7}, {16, -3}, {17, -4}, { 5, 19}, {19, -8},
        { 3, 16}, {12, 13}, { 3, -4}, {17,  5}, {-3, 15},
        {-3, -9}, { 0, 11}, {-9, -3}, {-4, -2}, {12, 10}
    };
    int hsize;
    Point* hull = convexHull(points, sizeof(points)/sizeof(Point), &hsize);
    printf("Convex Hull: ");
    printPoints(hull, hsize);
    printf("\n");
    free(hull);
 
    return 0;
}

Go: package main

import (
	"fmt"
	"image"
	"sort"
)




func (p points) ConvexHull() points {
	
	
	sort.Sort(p)
	var h points

	
	for _, pt := range p {
		for len(h) >= 2 && !ccw(h[len(h)-2], h[len(h)-1], pt) {
			h = h[:len(h)-1]
		}
		h = append(h, pt)
	}

	
	for i, t := len(p)-2, len(h)+1; i >= 0; i-- {
		pt := p[i]
		for len(h) >= t && !ccw(h[len(h)-2], h[len(h)-1], pt) {
			h = h[:len(h)-1]
		}
		h = append(h, pt)
	}

	return h[:len(h)-1]
}


func ccw(a, b, c image.Point) bool {
	return ((b.X - a.X) * (c.Y - a.Y)) > ((b.Y - a.Y) * (c.X - a.X))
}

type points []image.Point

func (p points) Len() int      { return len(p) }
func (p points) Swap(i, j int) { p[i], p[j] = p[j], p[i] }
func (p points) Less(i, j int) bool {
	if p[i].X == p[j].X {
		return p[i].Y < p[i].Y
	}
	return p[i].X < p[j].X
}

func main() {
	pts := points{
		{16, 3}, {12, 17}, {0, 6}, {-4, -6}, {16, 6},
		{16, -7}, {16, -3}, {17, -4}, {5, 19}, {19, -8},
		{3, 16}, {12, 13}, {3, -4}, {17, 5}, {-3, 15},
		{-3, -9}, {0, 11}, {-9, -3}, {-4, -2}, {12, 10},
	}
	hull := pts.ConvexHull()
	fmt.Println("Convex Hull:", hull)
}