LeetCode | Combinations

퉀
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],
]

ÓÃdfs/µÝ¹é»ñµÃËùÓÐ×éºÏ¡£

´úÂë

import java.util.ArrayList;

public class Combinations {
	private ArrayList
  
   > results;
	private int n;
	private int k;

	public ArrayList
   
    > combine(int n, int k) { results = new ArrayList
    
     >(); this.n = n; this.k = k; dfs(0, 1, new ArrayList
     
      ()); return results; } private void dfs(int level, int start, ArrayList
      
        list) { if (level == k) { results.add(new ArrayList
       
        (list)); return; } for (int i = start; i <= n; ++i) { ArrayList
        
          temp = new ArrayList
         
          (list); temp.add(i); dfs(level + 1, i + 1, temp); } } }