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Combinations

Tags : array, backtracking, leetcode, cpp, medium

Problem Statement - link #

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.

Examples #

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 #

Solutions #


class Solution {
public:
    void bt(vector<vector<int>> &res,vector<int> &tmp,int i,int k,int n){
        if(tmp.size() == k){
            res.push_back(tmp); 
            return ;
        }
        for(int j=i; j<=n; j++){
            tmp.push_back(j);
            bt(res,tmp,j+1,k,n);
            tmp.pop_back();
        }
        
    }
    vector<vector<int>> combine(int n, int k) {
        vector<vector<int>> res;
        vector<int> tmp;
        bt(res,tmp,1,k,n);
        return res;
    }
   
};