Minimize rope length to connect given points in a 3D plane

// C++ code for the above approach:
#include <bits/stdc++.h>
using namespace std;
vector<vector<int> > edges;

int findparent(int a, vector<int>& parentOf)
{
	if (parentOf[a] == -1)
		return a;
	return parentOf[a] = findparent(parentOf[a], parentOf);
}

void union_set(int a, int b, vector<int>& parentOf,
			vector<int>& rank)
{
	int s1 = findparent(a, parentOf);
	int s2 = findparent(b, parentOf);

	if (s1 != s2) {
		int r1 = rank[s1];
		int r2 = rank[s2];
		if (r1 >= r2) {
			parentOf[s2] = s1;
			rank[s1] = r1 + r2;
		}
		else {
			parentOf[s1] = s2;
			rank[s2] = r1 + r2;
		}
	}
}
int calculatemst(int N)
{
	int cost = 0;
	vector<int> rank(N + 1, -1);
	vector<int> parentOf(N + 1, -1);
	for (int i = 0; i < edges.size(); i++) {
		int wt = edges[i][0], a = edges[i][1],
			b = edges[i][2];
		if (findparent(a, parentOf)
			!= findparent(b, parentOf)) {
			cost += wt;
			union_set(a, b, parentOf, rank);
		}
	}
	return cost;
}
void graph(vector<pair<int, int> > v)
{
	for (int i = 0; i < v.size() - 1; i++) {
		int dist = v[i + 1].first - v[i].first;
		int nodeone = v[i].second;
		int nodesecond = v[i + 1].second;
		edges.push_back({ dist, nodeone, nodesecond });
	}
}
void solve(int a[][3], int N)
{
	vector<pair<int, int> > x, y, z;
	for (int i = 0; i < N; i++) {
		x.push_back({ a[i][0], i + 1 });
		y.push_back({ a[i][1], i + 1 });
		z.push_back({ a[i][2], i + 1 });
	}
	sort(x.begin(), x.end());
	sort(y.begin(), y.end());
	sort(z.begin(), z.end());
	graph(x);
	graph(y);
	graph(z);
	sort(edges.begin(), edges.end());
	return;
}

// Drivers code
int main()
{
	int arr[][3] = {
		{ 1, 2, 3 }, { 6, 8, 1 }, { 5, 3, 4 }, { 8, 5, 6 }
	};

	// Function Call
	solve(arr, 4);
	cout << calculatemst(4) << endl;
}