77. Combinations | LeetCode Solution

  77. Combinations | LeetCode Solution

Given two integers n and k, return all possible combinations of k numbers out of the range [1, n].

You may return the answer in any order.

 

Example 1:

Input: n = 4, k = 2
Output:
[
  [2,4],
  [3,4],
  [2,3],
  [1,2],
  [1,3],
  [1,4],
]

Example 2:

Input: n = 1, k = 1
Output: [[1]]

 

Constraints:

• 1 <= n <= 20
• 1 <= k <= n

class Solution

{

public:

  vector<vector<int>> combine(int n, int k)

  {

    vector<vector<int>> result;

    int i = 0;

    vector<int> p(k, 0);

    while (i >= 0)

    {

      p[i]++;

      if (p[i] > n)

        --i;

      else if (i == k - 1)

        result.push_back(p);

      else

      {

        ++i;

        p[i] = p[i - 1];

      }

    }

    return result;

  }

};