Given four integers n, w, m and k where,

- m is the total number of men.
- w is the total number of women.
- n is the total number of people that need to be selected to form the team.
- k is the minimum number of men that have to be selected.

The task is to find the number of ways in which the team can be formed.

**Examples:**

Input:m = 2, w = 2, n = 3, k = 1

Output:4

There are 2 men, 2 women. We need to make a team of size 3 with at least one man and one woman. We can make the team in following ways.

m1 m2 w1

m1 w1 w2

m2 w1 w2

m1 m2 w2

Input:m = 7, w = 6, n = 5, k = 3

Output:756

Input:m = 5, w = 6, n = 6, k = 3

Output:281

**Approach:** Since, we have to take at least k men.

Totals ways = Ways when ‘k’ men are selected + Ways when ‘k+1’ men are selected + … + when ‘n’ men are selected

.

Taking the first example from above where out of 7 men and 6 women, total 5 people need to be selected with at least 3 men,

Number of ways = (7C3 x 6C2) + (7C4 x 6C1) + (7C5)

= 7 x 6 x 5 x 6 x 5 + (7C3 x 6C1) + (7C2)

= 525 + 7 x 6 x 5 x 6 + 7 x 6

= (525 + 210 + 21)

= 756

Below is the implementation of the above approach:

## C++

`// C++ implementation of the approach ` `#include <bits/stdc++.h> ` `using` `namespace` `std; ` ` ` `// Returns factorial ` `// of the number ` `int` `fact(` `int` `n) ` `{ ` ` ` `int` `fact = 1; ` ` ` `for` `(` `int` `i = 2; i <= n; i++) ` ` ` `fact *= i; ` ` ` `return` `fact; ` `} ` ` ` `// Function to calculate ncr ` `int` `ncr(` `int` `n, ` `int` `r) ` `{ ` ` ` `int` `ncr = fact(n) / (fact(r) * fact(n - r)); ` ` ` `return` `ncr; ` `} ` ` ` `// Function to calculate ` `// the total possible ways ` `int` `ways(` `int` `m, ` `int` `w, ` `int` `n, ` `int` `k) ` `{ ` ` ` ` ` `int` `ans = 0; ` ` ` `while` `(m >= k) { ` ` ` `ans += ncr(m, k) * ncr(w, n - k); ` ` ` `k += 1; ` ` ` `} ` ` ` ` ` `return` `ans; ` `} ` ` ` `// Driver code ` `int` `main() ` `{ ` ` ` ` ` `int` `m, w, n, k; ` ` ` `m = 7; ` ` ` `w = 6; ` ` ` `n = 5; ` ` ` `k = 3; ` ` ` `cout << ways(m, w, n, k); ` `} ` |

## Java

`// Java implementation of the approach ` ` ` `import` `java.io.*; ` ` ` `class` `GFG { ` ` ` `// Returns factorial ` `// of the number ` `static` `int` `fact(` `int` `n) ` `{ ` ` ` `int` `fact = ` `1` `; ` ` ` `for` `(` `int` `i = ` `2` `; i <= n; i++) ` ` ` `fact *= i; ` ` ` `return` `fact; ` `} ` ` ` `// Function to calculate ncr ` `static` `int` `ncr(` `int` `n, ` `int` `r) ` `{ ` ` ` `int` `ncr = fact(n) / (fact(r) * fact(n - r)); ` ` ` `return` `ncr; ` `} ` ` ` `// Function to calculate ` `// the total possible ways ` `static` `int` `ways(` `int` `m, ` `int` `w, ` `int` `n, ` `int` `k) ` `{ ` ` ` ` ` `int` `ans = ` `0` `; ` ` ` `while` `(m >= k) { ` ` ` `ans += ncr(m, k) * ncr(w, n - k); ` ` ` `k += ` `1` `; ` ` ` `} ` ` ` ` ` `return` `ans; ` `} ` ` ` `// Driver code ` ` ` `public` `static` `void` `main (String[] args) { ` ` ` ` ` `int` `m, w, n, k; ` ` ` `m = ` `7` `; ` ` ` `w = ` `6` `; ` ` ` `n = ` `5` `; ` ` ` `k = ` `3` `; ` ` ` `System.out.println( ways(m, w, n, k)); ` ` ` `} ` `} ` `// This Code is contributed ` `// by shs ` |

## Python3

`# Python 3 implementation of the approach ` ` ` `# Returns factorial of the number ` `def` `fact(n): ` ` ` `fact ` `=` `1` ` ` `for` `i ` `in` `range` `(` `2` `, n ` `+` `1` `): ` ` ` `fact ` `*` `=` `i ` ` ` `return` `fact ` ` ` `# Function to calculate ncr ` `def` `ncr(n, r): ` ` ` `ncr ` `=` `fact(n) ` `/` `/` `(fact(r) ` `*` `fact(n ` `-` `r)) ` ` ` `return` `ncr ` ` ` `# Function to calculate ` `# the total possible ways ` `def` `ways(m, w, n, k): ` ` ` `ans ` `=` `0` ` ` `while` `(m >` `=` `k): ` ` ` `ans ` `+` `=` `ncr(m, k) ` `*` `ncr(w, n ` `-` `k) ` ` ` `k ` `+` `=` `1` ` ` ` ` `return` `ans; ` ` ` `# Driver code ` `m ` `=` `7` `w ` `=` `6` `n ` `=` `5` `k ` `=` `3` `print` `(ways(m, w, n, k)) ` ` ` `# This code is contributed by sahishelangia ` |

## C#

`// C# implementation of the approach ` ` ` `class` `GFG { ` ` ` `// Returns factorial ` `// of the number ` `static` `int` `fact(` `int` `n) ` `{ ` ` ` `int` `fact = 1; ` ` ` `for` `(` `int` `i = 2; i <= n; i++) ` ` ` `fact *= i; ` ` ` `return` `fact; ` `} ` ` ` `// Function to calculate ncr ` `static` `int` `ncr(` `int` `n, ` `int` `r) ` `{ ` ` ` `int` `ncr = fact(n) / (fact(r) * fact(n - r)); ` ` ` `return` `ncr; ` `} ` ` ` `// Function to calculate ` `// the total possible ways ` `static` `int` `ways(` `int` `m, ` `int` `w, ` `int` `n, ` `int` `k) ` `{ ` ` ` ` ` `int` `ans = 0; ` ` ` `while` `(m >= k) { ` ` ` `ans += ncr(m, k) * ncr(w, n - k); ` ` ` `k += 1; ` ` ` `} ` ` ` ` ` `return` `ans; ` `} ` ` ` `// Driver code ` ` ` `static` `void` `Main () { ` ` ` ` ` `int` `m, w, n, k; ` ` ` `m = 7; ` ` ` `w = 6; ` ` ` `n = 5; ` ` ` `k = 3; ` ` ` `System.Console.WriteLine( ways(m, w, n, k)); ` ` ` `} ` `} ` `// This Code is contributed by mits ` |

## PHP

`<?php ` `// PHP implementation of the approach ` ` ` `// Returns factorial of the number ` `function` `fact(` `$n` `) ` `{ ` ` ` `$fact` `= 1; ` ` ` `for` `(` `$i` `= 2; ` `$i` `<= ` `$n` `; ` `$i` `++) ` ` ` `$fact` `*= ` `$i` `; ` ` ` `return` `$fact` `; ` `} ` ` ` `// Function to calculate ncr ` `function` `ncr(` `$n` `, ` `$r` `) ` `{ ` ` ` `$ncr` `= (int)(fact(` `$n` `) / (fact(` `$r` `) * ` ` ` `fact(` `$n` `- ` `$r` `))); ` ` ` `return` `$ncr` `; ` `} ` ` ` `// Function to calculate the total ` `// possible ways ` `function` `ways(` `$m` `, ` `$w` `, ` `$n` `, ` `$k` `) ` `{ ` ` ` `$ans` `= 0; ` ` ` `while` `(` `$m` `>= ` `$k` `) ` ` ` `{ ` ` ` `$ans` `+= ncr(` `$m` `, ` `$k` `) * ` ` ` `ncr(` `$w` `, ` `$n` `- ` `$k` `); ` ` ` `$k` `+= 1; ` ` ` `} ` ` ` ` ` `return` `$ans` `; ` `} ` ` ` `// Driver code ` `$m` `= 7; ` `$w` `= 6; ` `$n` `= 5; ` `$k` `= 3; ` `echo` `ways(` `$m` `, ` `$w` `, ` `$n` `, ` `$k` `); ` ` ` `// This Code is contributed ` `// by Mukul Singh ` |

**Output:**

756

**Further Optimization : **The above code can be optimized using faster algorithms for binomial coefficient computation.

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