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  • LeetCode

    题目:

    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],
    ]
    

    思路:

    递归

    package recursion;
    
    import java.util.ArrayList;
    import java.util.List;
    
    public class Combinations {
    
        public List<List<Integer>> combine(int n, int k) {
            List<List<Integer>> res = new ArrayList<List<Integer>>();
            List<Integer> record = new ArrayList<Integer>();
            generateRecord(res, record, 1, n, k);
            return res;
        }
        
        private void generateRecord(List<List<Integer>> res, List<Integer> record, int start, int end, int k) {
            if (k == 0) {
                res.add(record);
                return;
            }
            
            for (int i = start; i <= end - k + 1; ++i) { 
                List<Integer> newRecord = new ArrayList<Integer>(record);
                newRecord.add(i);
                generateRecord(res, newRecord, i + 1, end, k - 1);
            }
        }
        
        public static void main(String[] args) {
            // TODO Auto-generated method stub
            Combinations c = new Combinations();
            List<List<Integer>> res = c.combine(4, 2);
            for (List<Integer> l : res) {
                for (int i : l) 
                    System.out.print(i + "	");
                System.out.println();
            }
        }
    
    }
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  • 原文地址:https://www.cnblogs.com/null00/p/5094656.html
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