# Number of parallelograms when n horizontal parallel lines intersect m vertical parallellines

Given two positive integers n and m. The task is to count number of parallelogram that can be formed of any size when n horizontal parallel lines intersect with m vertical parallel lines.

Examples:

```Input : n = 3, m = 2
Output : 3
2 parallelograms of size 1x1 and 1 parallelogram
of size 2x1.

Input : n = 5, m = 5
Output : 100
```

## Recommended: Please try your approach on {IDE} first, before moving on to the solution.

The idea is to use Combination, which state, number of ways to choose k items from given n items is given by nCr.
To form a parallelogram, we need two horizontal parallel lines and two vertical parallel lines. So, number of ways to choose two horizontal parallel lines are nC2 and number of ways to choose two vertical parallel lines are mC2. So, total number of possible parallelogram will be nC2 x mC2.

Below is C++ implementation of this approach:

## C++

 `// CPP Program to find number of parallelogram when  ` `// n horizontal parallel lines intersect m vertical  ` `// parallel lines. ` `#include ` `#define MAX 10 ` `using` `namespace` `std; ` ` `  `// Find value of Binomial Coefficient ` `int` `binomialCoeff(``int` `C[][MAX], ``int` `n, ``int` `k) ` `{  ` `    ``// Calculate value of Binomial Coefficient ` `    ``// in bottom up manner ` `    ``for` `(``int` `i = 0; i <= n; i++) ` `    ``{ ` `        ``for` `(``int` `j = 0; j <= min(i, k); j++) ` `        ``{ ` `            ``// Base Cases ` `            ``if` `(j == 0 || j == i) ` `                ``C[i][j] = 1; ` `  `  `            ``// Calculate value using previously ` `            ``// stored values ` `            ``else` `                ``C[i][j] = C[i-1][j-1] + C[i-1][j]; ` `        ``} ` `    ``} ` `} ` ` `  `// Return number of parallelogram when n horizontal ` `// parallel lines intersect m vertical parallel lines. ` `int` `countParallelogram(``int` `n, ``int` `m) ` `{ ` `    ``int`  `C[MAX][MAX] = { 0 };     ` `    ``binomialCoeff(C, max(n, m), 2);     ` `    ``return` `C[n][2] * C[m][2]; ` `} ` ` `  `// Driver Program ` `int` `main() ` `{ ` `    ``int` `n = 5, m = 5;     ` `    ``cout << countParallelogram(n, m) << endl; ` `    ``return` `0; ` `}  `

## Java

 `// Java Program to find number of parallelogram when  ` `// n horizontal parallel lines intersect m vertical  ` `// parallel lines. ` `class` `GFG ` `{ ` `    ``static` `final` `int` `MAX = ``10``; ` `     `  `    ``// Find value of Binomial Coefficient ` `    ``static` `void` `binomialCoeff(``int` `C[][], ``int` `n, ``int` `k) ` `    ``{  ` `        ``// Calculate value of Binomial Coefficient ` `        ``// in bottom up manner ` `        ``for` `(``int` `i = ``0``; i <= n; i++) ` `        ``{ ` `            ``for` `(``int` `j = ``0``; j <= Math.min(i, k); j++) ` `            ``{ ` `                ``// Base Cases ` `                ``if` `(j == ``0` `|| j == i) ` `                    ``C[i][j] = ``1``; ` `     `  `                ``// Calculate value using previously ` `                ``// stored values ` `                ``else` `                    ``C[i][j] = C[i - ``1``][j - ``1``] + C[i - ``1``][j]; ` `            ``} ` `        ``} ` `    ``} ` `     `  `    ``// Return number of parallelogram when n horizontal ` `    ``// parallel lines intersect m vertical parallel lines. ` `    ``static` `int` `countParallelogram(``int` `n, ``int` `m) ` `    ``{ ` `        ``int` `C[][]=``new` `int``[MAX][MAX];  ` `         `  `        ``binomialCoeff(C, Math.max(n, m), ``2``);  ` `         `  `        ``return` `C[n][``2``] * C[m][``2``]; ` `    ``} ` `     `  `    ``// Driver code ` `    ``public` `static` `void` `main(String arg[])  ` `    ``{ ` `        ``int` `n = ``5``, m = ``5``;  ` `        ``System.out.println(countParallelogram(n, m)); ` `    ``} ` `} ` ` `  `// This code is contributed By Anant Agarwal. `

/div>

## C#

 `// C# Program to find number of parallelogram when  ` `// n horizontal parallel lines intersect m vertical  ` `// parallel lines. ` `using` `System; ` ` `  `class` `GFG ` `{ ` `    ``static` `int` `MAX = 10; ` `     `  `    ``// Find value of Binomial Coefficient ` `    ``static` `void` `binomialCoeff(``int` `[,]C, ``int` `n, ``int` `k) ` `    ``{  ` `        ``// Calculate value of Binomial Coefficient ` `        ``// in bottom up manner ` `        ``for` `(``int` `i = 0; i <= n; i++) ` `        ``{ ` `            ``for` `(``int` `j = 0; j <= Math.Min(i, k); j++) ` `            ``{ ` `                ``// Base Cases ` `                ``if` `(j == 0 || j == i) ` `                    ``C[i, j] = 1; ` `     `  `                ``// Calculate value using previously ` `                ``// stored values ` `                ``else` `                    ``C[i, j] = C[i - 1, j - 1] + C[i - 1, j]; ` `            ``} ` `        ``} ` `    ``} ` `     `  `    ``// Return number of parallelogram when n horizontal ` `    ``// parallel lines intersect m vertical parallel lines. ` `    ``static` `int` `countParallelogram(``int` `n, ``int` `m) ` `    ``{ ` `        ``int` `[,]C = ``new` `int``[MAX, MAX];  ` `         `  `        ``binomialCoeff(C, Math.Max(n, m), 2);  ` `         `  `        ``return` `C[n, 2] * C[m, 2]; ` `    ``} ` `     `  `    ``// Driver code ` `    ``public` `static` `void` `Main()  ` `    ``{ ` `        ``int` `n = 5, m = 5;  ` `        ``Console.WriteLine(countParallelogram(n, m)); ` `    ``} ` `} ` ` `  `// This code is contributed By vt_m. `

Output:

```100
```

## tags:

Geometric Geometric