# Count the number of ways to divide N in k groups incrementally

Given two integers N and K, the task is to count the number of ways to divide N into K groups of positive integers such that their sum is N and the number of elements in groups follows a non-decreasing order (i.e group[i] <= group[i+1]).
Examples:

Input: N = 8, K = 4
Output:
Explanation:
Their are 5 groups such that their sum is 8 and the number of positive integers in each group is 4.
[1, 1, 1, 5], [1, 1, 2, 4], [1, 1, 3, 3], [1, 2, 2, 3], [2, 2, 2, 2]
Input: N = 24, K = 5
Output: 164
Explanation:
There are 164 such groups such that their sum is 24 and number of positive integers in each group is 5

Naive Approach: We can solve this problem using recursion. At each step of recursion put all the values greater than equal to the previously computed value.
Below is the implementation of the above approach:

## C++

 `// C++ implementation to count the` `// number of ways to divide N in ` `// groups such that each group ` `// has K number of elements`   `#include `   `using` `namespace` `std;`   `// Function to count the number` `// of ways to divide the number N` `// in groups such that each group` `// has K number of elements` `int` `calculate(``int` `pos, ``int` `prev, ` `                 ``int` `left, ``int` `k)` `{` `    ``// Base Case` `    ``if` `(pos == k) {` `        ``if` `(left == 0)` `            ``return` `1;` `        ``else` `            ``return` `0;` `    ``}`   `    ``// if N is divides completely` `    ``// into less than k groups` `    ``if` `(left == 0)` `        ``return` `0;`   `    ``int` `answer = 0;` `    `  `    ``// put all possible values ` `    ``// greater equal to prev` `    ``for` `(``int` `i = prev; i <= left; i++) {` `        ``answer += calculate(pos + 1, i, ` `                          ``left - i, k);` `    ``}` `    ``return` `answer;` `}`   `// Function to count the number of ` `// ways to divide the number N` `int` `countWaystoDivide(``int` `n, ``int` `k)` `{` `    ``return` `calculate(0, 1, n, k);` `}`   `// Driver Code` `int` `main()` `{` `    ``int` `N = 8;` `    ``int` `K = 4;`   `    ``cout << countWaystoDivide(N, K);` `    ``return` `0;` `}`

## Java

 `// Java implementation to count the` `// number of ways to divide N in ` `// groups such that each group ` `// has K number of elements` `import` `java.util.*;` `class` `GFG{`   `// Function to count the number` `// of ways to divide the number N` `// in groups such that each group` `// has K number of elements` `static` `int` `calculate(``int` `pos, ``int` `prev, ` `                     ``int` `left, ``int` `k)` `{` `    `  `    ``// Base Case` `    ``if` `(pos == k)` `    ``{` `        ``if` `(left == ``0``)` `            ``return` `1``;` `        ``else` `            ``return` `0``;` `    ``}`   `    ``// If N is divides completely` `    ``// into less than k groups` `    ``if` `(left == ``0``)` `        ``return` `0``;`   `    ``int` `answer = ``0``;` `    `  `    ``// Put all possible values ` `    ``// greater equal to prev` `    ``for``(``int` `i = prev; i <= left; i++) ` `    ``{` `       ``answer += calculate(pos + ``1``, i, ` `                           ``left - i, k);` `    ``}` `    ``return` `answer;` `}`   `// Function to count the number of ` `// ways to divide the number N` `static` `int` `countWaystoDivide(``int` `n, ``int` `k)` `{` `    ``return` `calculate(``0``, ``1``, n, k);` `}`   `// Driver Code` `public` `static` `void` `main(String[] args)` `{` `    ``int` `N = ``8``;` `    ``int` `K = ``4``;`   `    ``System.out.print(countWaystoDivide(N, K));` `}` `}`   `// This code is contributed by Rajput-Ji`

## Python3

 `# Python3 implementation to count the` `# number of ways to divide N in` `# groups such that each group` `# has K number of elements`   `# Function to count the number` `# of ways to divide the number N` `# in groups such that each group` `# has K number of elements` `def` `calculate(pos, prev, left, k):` `    `  `    ``# Base Case` `    ``if` `(pos ``=``=` `k):` `        ``if` `(left ``=``=` `0``):` `            ``return` `1``;` `        ``else``:` `            ``return` `0``;`   `    ``# If N is divides completely` `    ``# into less than k groups` `    ``if` `(left ``=``=` `0``):` `        ``return` `0``;`   `    ``answer ``=` `0``;`   `    ``# Put all possible values` `    ``# greater equal to prev` `    ``for` `i ``in` `range``(prev, left ``+` `1``):` `        ``answer ``+``=` `calculate(pos ``+` `1``, i,` `                           ``left ``-` `i, k);`   `    ``return` `answer;`   `# Function to count the number of` `# ways to divide the number N` `def` `countWaystoDivide(n, k):` `    `  `    ``return` `calculate(``0``, ``1``, n, k);`   `# Driver Code` `if` `__name__ ``=``=` `'__main__'``:` `    `  `    ``N ``=` `8``;` `    ``K ``=` `4``;`   `    ``print``(countWaystoDivide(N, K));`   `# This code is contributed by 29AjayKumar`

## C#

 `// C# implementation to count the` `// number of ways to divide N in ` `// groups such that each group ` `// has K number of elements` `using` `System;`   `class` `GFG{`   `// Function to count the number` `// of ways to divide the number N` `// in groups such that each group` `// has K number of elements` `static` `int` `calculate(``int` `pos, ``int` `prev, ` `                     ``int` `left, ``int` `k)` `{` `    `  `    ``// Base Case` `    ``if` `(pos == k)` `    ``{` `        ``if` `(left == 0)` `            ``return` `1;` `        ``else` `            ``return` `0;` `    ``}`   `    ``// If N is divides completely` `    ``// into less than k groups` `    ``if` `(left == 0)` `        ``return` `0;`   `    ``int` `answer = 0;` `    `  `    ``// Put all possible values ` `    ``// greater equal to prev` `    ``for``(``int` `i = prev; i <= left; i++) ` `    ``{` `       ``answer += calculate(pos + 1, i, ` `                           ``left - i, k);` `    ``}` `    ``return` `answer;` `}`   `// Function to count the number of ` `// ways to divide the number N` `static` `int` `countWaystoDivide(``int` `n, ``int` `k)` `{` `    ``return` `calculate(0, 1, n, k);` `}`   `// Driver Code` `public` `static` `void` `Main(String[] args)` `{` `    ``int` `N = 8;` `    ``int` `K = 4;`   `    ``Console.Write(countWaystoDivide(N, K));` `}` `}`   `// This code is contributed by Rajput-Ji`

Output:

```5

```

Time complexity: O(NK)
Efficient Approach: In the previous approach we can see that we are solving the subproblems repeatedly, i.e. it follows the property of Overlapping Subproblems. So we can memoize the same using DP table.
Below is the implementation of the above approach:

## C++

 `// C++ implementation to count the` `// number of ways to divide N in ` `// groups such that each group ` `// has K number of elements`   `#include `   `using` `namespace` `std;`   `// DP Table` `int` `dp;`   `// Function to count the number` `// of ways to divide the number N` `// in groups such that each group` `// has K number of elements` `int` `calculate(``int` `pos, ``int` `prev, ` `                ``int` `left, ``int` `k)` `{` `    ``// Base Case` `    ``if` `(pos == k) {` `        ``if` `(left == 0)` `            ``return` `1;` `        ``else` `            ``return` `0;` `    ``}` `    ``// if N is divides completely ` `    ``// into less than k groups` `    ``if` `(left == 0)` `        ``return` `0;`   `    ``// If the subproblem has been` `    ``// solved, use the value` `    ``if` `(dp[pos][prev][left] != -1)` `        ``return` `dp[pos][prev][left];`   `    ``int` `answer = 0;` `    ``// put all possible values ` `    ``// greater equal to prev` `    ``for` `(``int` `i = prev; i <= left; i++) {` `        ``answer += calculate(pos + 1, i, ` `                           ``left - i, k);` `    ``}`   `    ``return` `dp[pos][prev][left] = answer;` `}`   `// Function to count the number of ` `// ways to divide the number N in groups` `int` `countWaystoDivide(``int` `n, ``int` `k)` `{` `    ``// Intialize DP Table as -1` `    ``memset``(dp, -1, ``sizeof``(dp));`   `    ``return` `calculate(0, 1, n, k);` `}`   `// Driver Code` `int` `main()` `{` `    ``int` `N = 8;` `    ``int` `K = 4;`   `    ``cout << countWaystoDivide(N, K);` `    ``return` `0;` `}`

## Java

 `// Java implementation to count the` `// number of ways to divide N in ` `// groups such that each group ` `// has K number of elements` `import` `java.util.*;` `class` `GFG{` ` `  `// DP Table` `static` `int` `[][][]dp = ``new` `int``[``500``][``500``][``500``];` ` `  `// Function to count the number` `// of ways to divide the number N` `// in groups such that each group` `// has K number of elements` `static` `int` `calculate(``int` `pos, ``int` `prev, ` `                     ``int` `left, ``int` `k)` `{` `    ``// Base Case` `    ``if` `(pos == k) ` `    ``{` `        ``if` `(left == ``0``)` `            ``return` `1``;` `        ``else` `            ``return` `0``;` `    ``}` `  `  `    ``// if N is divides completely ` `    ``// into less than k groups` `    ``if` `(left == ``0``)` `        ``return` `0``;` ` `  `    ``// If the subproblem has been` `    ``// solved, use the value` `    ``if` `(dp[pos][prev][left] != -``1``)` `        ``return` `dp[pos][prev][left];` ` `  `    ``int` `answer = ``0``;` `  `  `    ``// put all possible values ` `    ``// greater equal to prev` `    ``for` `(``int` `i = prev; i <= left; i++) ` `    ``{` `        ``answer += calculate(pos + ``1``, i, ` `                           ``left - i, k);` `    ``}` ` `  `    ``return` `dp[pos][prev][left] = answer;` `}` ` `  `// Function to count the number of ` `// ways to divide the number N in groups` `static` `int` `countWaystoDivide(``int` `n, ``int` `k)` `{` `    ``// Intialize DP Table as -1` `        ``for` `(``int` `i = ``0``; i < ``500``; i++) ` `        ``{` `            ``for` `(``int` `j = ``0``; j < ``500``; j++)` `            ``{` `                ``for` `(``int` `l = ``0``; l < ``500``; l++)` `                    ``dp[i][j][l] = -``1``;` `            ``}` `        ``}` ` `  `    ``return` `calculate(``0``, ``1``, n, k);` `}` ` `  `// Driver Code` `public` `static` `void` `main(String[] args)` `{` `    ``int` `N = ``8``;` `    ``int` `K = ``4``;` ` `  `    ``System.out.print(countWaystoDivide(N, K));` `}` `}`   `// This code is contributed by Rajput-Ji`

## Python3

 `# Python3 implementation to count the` `# number of ways to divide N in` `# groups such that each group` `# has K number of elements` ` `  `# DP Table` `dp ``=` `[[[``0` `for` `i ``in` `range``(``50``)]` `             ``for` `j ``in` `range``(``50``)]` `          ``for` `j ``in` `range``(``50``)]`   `# Function to count the number` `# of ways to divide the number N` `# in groups such that each group` `# has K number of elements` `def` `calculate(pos, prev, left, k):` `   `  `    ``# Base Case` `    ``if` `(pos ``=``=` `k):` `        ``if` `(left ``=``=` `0``):` `            ``return` `1``;` `        ``else``:` `            ``return` `0``;` ` `  `    ``# if N is divides completely` `    ``# into less than k groups` `    ``if` `(left ``=``=` `0``):` `        ``return` `0``;` ` `  `    ``# If the subproblem has been` `    ``# solved, use the value` `    ``if` `(dp[pos][prev][left] !``=` `-``1``):` `        ``return` `dp[pos][prev][left];` ` `  `    ``answer ``=` `0``;` ` `  `    ``# put all possible values` `    ``# greater equal to prev` `    ``for` `i ``in` `range``(prev,left``+``1``):` `        ``answer ``+``=` `calculate(pos ``+` `1``, i, ` `                            ``left ``-` `i, k);` `    ``dp[pos][prev][left] ``=` `answer;` `    ``return` `dp[pos][prev][left];` ` `  `# Function to count the number of` `# ways to divide the number N in groups` `def` `countWaystoDivide(n, k):` `  `  `    ``# Intialize DP Table as -1` `    ``for` `i ``in` `range``(``50``):` `        ``for` `j ``in` `range``(``50``):` `            ``for` `l ``in` `range``(``50``):` `                ``dp[i][j][l] ``=` `-``1``;` ` `  `    ``return` `calculate(``0``, ``1``, n, k);` ` `  `# Driver Code` `if` `__name__ ``=``=` `'__main__'``:` `    ``N ``=` `8``;` `    ``K ``=` `4``;` ` `  `    ``print``(countWaystoDivide(N, K));` ` `  `# This code is contributed by Rajput-Ji`

## C#

 `// C# implementation to count the` `// number of ways to divide N in ` `// groups such that each group ` `// has K number of elements` `using` `System;` `class` `GFG{` ` `  `// DP Table` `static` `int` `[,,]dp = ``new` `int``[50, 50, 50];` ` `  `// Function to count the number` `// of ways to divide the number N` `// in groups such that each group` `// has K number of elements` `static` `int` `calculate(``int` `pos, ``int` `prev, ` `                     ``int` `left, ``int` `k)` `{` `    ``// Base Case` `    ``if` `(pos == k) ` `    ``{` `        ``if` `(left == 0)` `            ``return` `1;` `        ``else` `            ``return` `0;` `    ``}` `  `  `    ``// if N is divides completely ` `    ``// into less than k groups` `    ``if` `(left == 0)` `        ``return` `0;` ` `  `    ``// If the subproblem has been` `    ``// solved, use the value` `    ``if` `(dp[pos, prev, left] != -1)` `        ``return` `dp[pos, prev, left];` ` `  `    ``int` `answer = 0;` `  `  `    ``// put all possible values ` `    ``// greater equal to prev` `    ``for` `(``int` `i = prev; i <= left; i++) ` `    ``{` `        ``answer += calculate(pos + 1, i, ` `                           ``left - i, k);` `    ``}` ` `  `    ``return` `dp[pos, prev, left] = answer;` `}` ` `  `// Function to count the number of ` `// ways to divide the number N in groups` `static` `int` `countWaystoDivide(``int` `n, ``int` `k)` `{` `    ``// Intialize DP Table as -1` `        ``for` `(``int` `i = 0; i < 50; i++) ` `        ``{` `            ``for` `(``int` `j = 0; j < 50; j++)` `            ``{` `                ``for` `(``int` `l = 0; l < 50; l++)` `                    ``dp[i, j, l] = -1;` `            ``}` `        ``}` ` `  `    ``return` `calculate(0, 1, n, k);` `}` ` `  `// Driver Code` `public` `static` `void` `Main(String[] args)` `{` `    ``int` `N = 8;` `    ``int` `K = 4;` ` `  `    ``Console.Write(countWaystoDivide(N, K));` `}` `}`   `// This code is contributed by gauravrajput1`

Output:

`5`

Time complexity : O(N2 * K) My Personal Notes arrow_drop_up Check out this Author's contributed articles.

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