Need to find 3 points that make up the largest perimeter - c++

Question

I have a structure called point. Obviously, it provides coordinates of a point( x and y). I have an array of points.
What I need to do is find 3 points that make up the largest triangle. I've tried a lot of options and I didn't make it.
Can you think of an algorithm that would create the outcome I need?
#include "stdafx.h"
#include <iostream>
#include <vector>
using namespace std;
struct point {
double x, y;
};
int main()
{
double n, c1, c2;
double max(0), max1(0), max2(0), temp;
point *a = NULL;
cout << "Enter the number of points: ";
cin >> n;
a = new point[n];
for (int i = 0; i < n; i++) {
cin >> c1 >> c2;
point dot;
dot.x = c1;
dot.y = c2;
a[i] = dot;
};
for (int i = 0; i < n-1; i++) { // here I'm running out of ideas
for (int j = 1; j < n; j++) {
temp = sqrt((a[i].x + a[i].y)*(a[i].x + a[i].y)- (a[j].x + a[j].y)*(a[j].x + a[j].y));
if (temp > max)
}
}

Answer 1

You can just iterate over all sets of three points. Note that it is better to use a vector instead of an array and it is useful to put the code to calculate the perimeter in a separate function
#include <iostream>
#include <vector>
#include <math.h>
using namespace std;
struct point {
double x, y;
};
double perim(point p1, point p2, point p3)
{
double result = 0;
result += sqrt(pow(p1.x - p2.x, 2) + pow(p1.y - p2.y, 2));
result += sqrt(pow(p2.x - p3.x, 2) + pow(p2.y - p3.y, 2));
result += sqrt(pow(p3.x - p1.x, 2) + pow(p3.y - p1.y, 2));
return result;
}
int main()
{
double n, c1, c2;
double max(0), temp;
int p1 = 0, p2 = 0, p3 = 0;
vector <point> a;
cout << "Enter the number of points: ";
cin >> n;
for (int i = 0; i < n; i++) {
cin >> c1 >> c2;
point dot;
dot.x = c1;
dot.y = c2;
a.push_back(dot);
};
for (int i = 0; i < n - 2; i++) { // here I'm running out of ideas
for (int j = i+1; j < n - 1; j++) {
for (int k = j+1; k < n; k++) {
temp = perim(a[i], a[j], a[k]);
if (temp > max) {
max = temp;
p1 = i; p2 = j; p3 = k;
}
}
}
}
cout << p1 << " "<<p2<< " "<<p3;
}