【LeetCode】77. 组合

客官°小女子只卖身不卖艺 2024-03-27 13:53 117阅读 0赞

> [牛客华为机试题库【题号 HJ开头】（重点看）][HJ]  
> [牛客在线编程算法篇【题号NC开头】][NC]  
> [剑指offer【题号 JZ开头】][offer_ JZ]  
> [力扣][Link 1]

### 1）[原题链接][Link 2] ###

### 2）已有题解 ###

### 3）代码 ###

package dfs;
    
    import java.io.BufferedReader;
    import java.io.IOException;
    import java.io.InputStreamReader;
    import java.util.*;
    
    import static java.lang.Integer.parseInt;
    import static java.lang.System.in;
    
    /**
     * LeetCode77. 组合
     * 范围 [1, n] 中所有可能的 k 个数的组合
     */
    public class Leetcode77Combinations {
        
    
        public static void main(String[] args) throws IOException {
        
            BufferedReader bf = new BufferedReader(new InputStreamReader(in));
            bf.close();
    
            int n = 5; // n个数，1,2,3,4,5
            int k = 3; // 任意三个的组合
            List<List<Integer>> res = combine(n, k);
            System.out.println(res);
        }
    
        /**
         * LeetCode77. 组合
         * 范围 [1, n] 中所有可能的 k 个数的组合
         */
        public static List<List<Integer>> combine(int n, int k) {
        
            // k<=0时没意义;
            // n<k时没意义,一共才n个想取k个不合理
            if (k <= 0 || n < k) {
        
                return new ArrayList<>();
            }
    
            List<List<Integer>> res = new ArrayList<>();
            Deque<Integer> stack = new LinkedList<>();
            dfs(1, n, k, stack, res);
    
            return res;
        }
    
        public static void dfs(int start, int milestone, int limit, Deque<Integer> stack, List<List<Integer>> res) {
        
            if (stack.size() == limit) {
        
                res.add(new ArrayList<>(stack));
                System.out.println(new ArrayList<>(stack));
                return;
            }
    
            for (int i = start; i <= milestone; i++) {
        
                stack.push(i);
                dfs(i + 1, milestone, limit, stack, res);
                stack.pop();
            }
        }
    }

[HJ]: https://www.nowcoder.com/exam/oj/ta?tpId=37
[NC]: https://www.nowcoder.com/exam/oj
[offer_ JZ]: https://www.nowcoder.com/exam/oj/ta?page=1&tpId=13&type=13
[Link 1]: https://leetcode.cn/problemset/all/
[Link 2]: https://leetcode.cn/problems/combinations/