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Combinations

Given two integers n and k, return all possible combinations ofk 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],
]

答案

public class Solution {
    public List<List<Integer>> combine(int n,int start,int k)
    {
        List<List<Integer>> result=new LinkedList<List<Integer>>();
        if(k==0)
        {
            result.add(new LinkedList<Integer>());
            return result;
        }
        for(;start<=n-k+1;start++)
        {
             List<List<Integer>> p=combine(n,start+1,k-1);
             for(List<Integer> element:p)
             {
                 element.add(0,start);
                 result.add(element);
             }
        }
        return result;
    }
    public List<List<Integer>> combine(int n, int k) {
        List<List<Integer>> result=combine(n,1,k);
        return result;
    }
}


Combinations