[LintCode/LeetCode] Combinations

Raaabbit 发布于2019-08-14 15:23 / 1434人阅读

摘要：题目为求从到的自然数里取个数的所有组合全集。使用递归的模板，建立函数。模板如下也可以不建立新的，而是递归调用之后删去中最后一个元素

Problem

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

Example

For example,
If n = 4 and k = 2, a solution is:
[[2,4],[3,4],[2,3],[1,2],[1,3],[1,4]]

Note

题目为求从1到n的自然数里取k个数的所有组合全集。使用递归的模板，建立helper函数。
模板如下：

</>复制代码 
void helper(range S, target T, start A, tempArray B) {
    if (B met T or other requirement) {
        res.add(B);
        return;
    }
    for (int i starts from A in S) {
        tempArray C = new tempArray (B);
        C.add(i);
        helper(S, T-i, i+1, C);
    }
}

也可以不建立新的tempArray C，而是递归调用helper之后删去B中最后一个元素：

</>复制代码 
void helper(range S, target T, start A, tempArray B) {
    if (B met T or other requirement) {
        res.add(B);
        return;
    }
    for (int i starts from A in S) {
        B.add(i);
        helper(S, T-i, i+1, C);
        B.remove(B.size()-1);
    }
}

Solution

</>复制代码 
public class Solution {
    List> res = new ArrayList>();
    public List> combine(int n, int k) {
        helper(n, k, 1, new ArrayList());
        return res;
    }
    private void helper(int n, int k, int start, List pre) {
        if (pre.size() == k) {
            res.add(pre);
            return;
        }
        for (int i = start; i <= n; i++) {
            List cur = new ArrayList (pre);
            cur.add(i);
            helper(n, k, i+1, cur);
        }
    }
}

GPU云服务器云服务器 Combinations

文章版权归作者所有，未经允许请勿转载,若此文章存在违规行为，您可以联系管理员删除。

转载请注明本文地址：https://www.ucloud.cn/yun/65722.html

[LintCode/LeetCode] Combination Sum I & II

摘要：和唯一的不同是组合中不能存在重复的元素，因此，在递归时将初始位即可。 Combination Sum I Problem Given a set of candidate numbers (C) and a target number (T), find all unique combinations in C where the candidate numbers sums to T...

ThreeWords 2019-08-14 15:23 评论0 收藏0
[LintCode/LeetCode] Restore IP Addresses

摘要：第一个分割点第二个分割点第三个分割点 Problem Given a string containing only digits, restore it by returning all possible valid IP address combinations. Example Given 25525511135, return [ 255.255.11.135, 255....

bingo 2019-08-14 15:14 评论0 收藏0
[LintCode/LeetCode] Word Break

Problem Given a string s and a dictionary of words dict, determine if s can be break into a space-separated sequence of one or more dictionary words. Example Given s = lintcode, dict = [lint, code]. R...

dunizb 2019-08-14 15:30 评论0 收藏0
[LintCode/LeetCode] First Unique Character in a S

Problem Given a string, find the first non-repeating character in it and return its index. If it doesnt exist, return -1. Example Given s = lintcode, return 0. Given s = lovelintcode, return 2. Tags A...

Xufc 2019-08-15 13:27 评论0 收藏0
[LintCode/LeetCode] Find Median From / Data Stream

摘要：建立两个堆，一个堆就是本身，也就是一个最小堆另一个要写一个，使之成为一个最大堆。我们把遍历过的数组元素对半分到两个堆里，更大的数放在最小堆，较小的数放在最大堆。同时，确保最大堆的比最小堆大，才能从最大堆的顶端返回。 Problem Numbers keep coming, return the median of numbers at every time a new number a...

zxhaaa 2019-08-14 14:35 评论0 收藏0