Combinations

Desicription

Given two integers n and k, return all possible combinations of k numbers out of 1 … n.

For example,

If n = 4 and k = 2, a solution is:

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[
  [2,4],
  [3,4],
  [2,3],
  [1,2],
  [1,3],
  [1,4],
]

Solution

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class Solution {
public:
    vector<vector<int>> combine(int n, int k) {
        vector<vector<int>> res;
        vector<int> tmp(k, 0);
        int index = 0;
        while(index >= 0){
            tmp[index]++;
            if(tmp[index] > n)
                index--;
            else if(index == k - 1)
                res.push_back(tmp);
            else
                index++, tmp[index] = tmp[index - 1];
        }
        return res;
    }
};