Find number of unique triangles among given N triangles in C++

In this problem, we are given three arrays s1[] , s2[] and s3[] of size N, denoting N triangles. Our task is to find the number of unique triangles among given N triangles.

For a triangle to be unique, all its side should be unique i.e. no other triangle should have the same sides.

Let’s take an example to understand the problem,

Input

s1[] = {1, 5, 3}
s2[] = {2, 3, 2}
s3[] = {4, 2, 5}

Output

1

Explanation

Triangle with sides 1 2 4 is unique.

Solution Approach

A simple solution to the problem is by counting the number of triangles which are unique.

For this, we will first sort each triangle’s side and then store in a map, if it’s values are unique increase the count.

Program to illustrate the working of our solution,

Example

Live Demo

#include <bits/stdc++.h>
using namespace std;
int countUniqueTriangle(int a[], int b[], int c[], int n) {
vector<int> triSides[n];
map<vector<int>, int> m;
for (int i = 0; i < n; i++) {
triSides[i].push_back(a[i]);
triSides[i].push_back(b[i]);
triSides[i].push_back(c[i]);
sort(triSides[i].begin(), triSides[i].end());
m[triSides[i]] = m[triSides[i]] + 1;
}
map<vector<int>, int>::iterator itr;
int uniqueTriCount = 0;
for (itr = m.begin(); itr != m.end(); itr++) {
if (itr->second == 1)
if (itr->second == 1)
uniqueTriCount++;
}
return uniqueTriCount;
}
int main() {
int s1[] = { 1, 5 ,3 };
int s2[] = { 2, 3, 2 };
int s3[] = { 4, 2, 5 };
int N = sizeof(s1) / sizeof(s1);
cout<<"The number of unique triangles is "<<countUniqueTriangle(s1, s2, s3, N);
return 0;
}

Output

The number of unique triangles is 1

Updated on: 15-Mar-2021

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