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;
}
};