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[Leetcode] Combinations

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:

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

 

Solution:

public class Solution {    public List<List<Integer>> combine(int n, int k) {        List<List<Integer>> result = new ArrayList<List<Integer>>();        List<Integer> temp = new ArrayList<Integer>();        dfs(n, k, 0, 1, result, temp);        return result;    }    private void dfs(int n, int k, int step, int start, List<List<Integer>> result, List<Integer> temp) {        // TODO Auto-generated method stub        if (step > k)            return;        if (step == k) {            result.add(new ArrayList<Integer>(temp));            return;        }        for(int i=start;i<=n;++i){            temp.add(i);            dfs(n, k, step+1, i+1, result, temp);            temp.remove(temp.size()-1);        }    }}

 

[Leetcode] Combinations