# Count number of right triangles possible with a given perimeter in C++

We are given a perimeter P of a triangle. Perimeter is the sum of all sides of the triangle. The goal is to find the number of right triangles that can be made which have the same perimeter.

If the sides of the triangle are a,b and c. Then a + b + c = P and a2 + b2 = c2 ( pythagoras theorem for any combination of a, b, and c )

We will check this by taking a from 1 to p/2 and b from a+1 to p/3. Then c = p-a-b (a+b+c=p)

For all right triangles, apply Pythagoras theorem. The values of a, b and c should also satisfy the condition of forming triangles where the sum of any two sides is always greater than third.

Let’s understand with examples.

Input − Perimeter P=12

Output − Total number of right triangles −1

Explanation

The only values of a, b and c which satisfy a+b+c=P and a2 + b2 = c2 ( also sum of any two > third ) are 4, 3, and 5.

4+3+5=12, 3*3+4*4=5*5 ( 9+16=25 ) also 3+4>5, 4+5>3, 3+5>4

Input − Perimeter P=10

Output − Total number of right triangles −0

Explanation

No values of a, b and c which could satisfy a+b+c=P and a2 + b2 = c2

## Approach used in the below program is as follows

• We take an integer variable perimeter which stores the value of the given perimeter.

• Function rightTriangles(int p) takes the perimeter as input and returns the total number of right triangles that are possible.

• Variable count stores the number of right triangles possible, initially 0.

• Using for loop start for a=1 to p/2

• Again using nested for loop start for b=a+1 to p/3 ( two sides are never equal in right triangles)

• Calculate c=p-a-b. For this a,b,c check if (a+b>c && b+c>a && a+c>b).

• Also check pythagoras theorem where a*a+b*b==c*c. If true increment count.

• At the end return count contains the number of right triangles possible with a given perimeter.

• Return count as desired result.

Note − we will check pythagoras theorem for only one combination of a,b and c for unique results.

## Example

Live Demo

#include <bits/stdc++.h>
using namespace std;
int rightTriangles(int p){
int count = 0;
int c=0;
for( int a=1;a<p/2;a++){
for(int b=1;b<p/3;b++){
c=p-a-b;
if( a+b>c && b+c>a && a+c>b) //condition for triangle{
if( (a*a+b*b)==c*c ) //pythagoras rule for right triangles
{ ++count; }
}
}
}
return count;
}
int main(){
int perimeter= 12;
cout << "Total number of right triangles that can be formed: "<<rightTriangles(perimeter);
return 0;
}

## Output

If we run the above code it will generate the following output −

Total number of right triangles that can be formed: 1

Updated on: 29-Aug-2020

165 Views