leetcode 77 Combinations
z
 2018-05-21 23:48:26  

Given two integers n and k, return all possible combinations of k numbers out of 1 … n.

Example:

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Input: n = 4, k = 2
Output:
[
  [2,4],
  [3,4],
  [2,3],
  [1,2],
  [1,3],
  [1,4],
]
  • bfs回溯就好了
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class Solution {
    public List<List<Integer>> combine(int n, int k) {
        List<List<Integer>> result = new ArrayList<List<Integer>>();
        List<Integer> current = new ArrayList<Integer>();
        bfs(result, current, n , k, 1);
        return result;
    }
    public void bfs(List<List<Integer>> result, List<Integer> current, int n, int k, int c){
        if(current.size() == k){
            result.add(new ArrayList<Integer>(current));
            return ;
        }
        for(int i=c; i<=n; i++){
            current.add(i);
            bfs(result, current, n ,k, ++c);
            current.remove(current.size()-1);
            
        }
    }
}