Convex Hull in Go

Convex

Hull in Go

Welcome to the Convex Hull in Go page! Here, you'll find the source code for this program as well as a description of how the program works.

Current Solution

package main

import (
	"fmt"
	"os"
	"sort"
	"strconv"
	"strings"
)

type Point struct {
	x int
	y int
}

const usage = `Usage: please provide at least 3 x and y coordinates as separate lists (e.g. "100, 440, 210")`

func parseCoordinates(input string) ([]int, error) {
	parts := strings.Split(input, ",")
	nums := make([]int, 0, len(parts))
	for _, p := range parts {
		val, err := strconv.Atoi(strings.TrimSpace(p))
		if err != nil {
			return nil, fmt.Errorf("invalid number %s", p)
		}
		nums = append(nums, val)
	}
	return nums, nil
}

func parsePoints(xArg, yArg string) ([]Point, error) {
	xs, errX := parseCoordinates(xArg)
	ys, errY := parseCoordinates(yArg)

	if errX != nil || errY != nil {
		return nil, fmt.Errorf("failed to parse input coordinates")
	}

	if len(xs) != len(ys) {
		return nil, fmt.Errorf("coordinate count mismatch: x=%d, y=%d", len(xs), len(ys))
	}

	if len(xs) < 3 {
		return nil, fmt.Errorf("at least 3 points are required")
	}

	points := make([]Point, len(xs))
	for i := 0; i < len(xs); i++ {
		points[i] = Point{x: xs[i], y: ys[i]}
	}
	return points, nil
}

func cross(o, a, b Point) int {
	return (a.x-o.x)*(b.y-o.y) - (a.y-o.y)*(b.x-o.x)
}

func convexHull(points []Point) []Point {
	n := len(points)
	if n <= 2 {
		return points
	}

	sort.Slice(points, func(i, j int) bool {
		if points[i].x != points[j].x {
			return points[i].x < points[j].x
		}
		return points[i].y < points[j].y
	})

	unique := points[:0]
	for i := 0; i < len(points); i++ {
		if i == 0 || points[i] != points[i-1] {
			unique = append(unique, points[i])
		}
	}
	points = unique

	if len(points) <= 2 {
		return points
	}

	var hull []Point

	for _, p := range points {
		for len(hull) >= 2 && cross(hull[len(hull)-2], hull[len(hull)-1], p) <= 0 {
			hull = hull[:len(hull)-1]
		}
		hull = append(hull, p)
	}

	lowerLen := len(hull)
	for i := len(points) - 2; i >= 0; i-- {
		p := points[i]
		for len(hull) > lowerLen && cross(hull[len(hull)-2], hull[len(hull)-1], p) <= 0 {
			hull = hull[:len(hull)-1]
		}
		hull = append(hull, p)
	}

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

func main() {
	if len(os.Args) != 3 {
		fmt.Fprintln(os.Stderr, usage)
		os.Exit(1)
	}

	points, err := parsePoints(os.Args[1], os.Args[2])
	if err != nil {
		fmt.Fprintf(os.Stderr, usage)
		os.Exit(1)
	}

	result := convexHull(points)

	for _, p := range result {
		fmt.Printf("(%d, %d)\n", p.x, p.y)
	}
}

Convex Hull in Go was written by:

• Ștefan-Iulian Alecu

If you see anything you'd like to change or update, please consider contributing.

How to Implement the Solution

No 'How to Implement the Solution' section available. Please consider contributing.

How to Run the Solution

No 'How to Run the Solution' section available. Please consider contributing.