LeetCode-Combinations

来源：互联网发布：自学编程语言知乎编辑：程序博客网时间：2024/06/05 06:56

题目：https://oj.leetcode.com/problems/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],]

源码：Java版本
算法分析：深搜，递归。时间复杂度O(n!)，空间复杂度O(n)

public class Solution {    public List<List<Integer>> combine(int n, int k) {        List<List<Integer>> results=new ArrayList<List<Integer>>();        Stack<Integer> stack=new Stack<Integer>();        combine(n,0,k,stack,results);        return results;    }        private void combine(int n,int start,int k,Stack<Integer> stack,            List<List<Integer>> results) {        if(k==0) {            results.add((Stack<Integer>)(stack.clone()));            return;        }        for(int i=start;i<n;i++) {            stack.push(i+1);            combine(n,i+1,k-1,stack,results);            stack.pop();        }    }}

0 0