77. Combinations

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Leetcode 77, 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], ] class Solution(object): def combine(self, n, k): """ :ty…

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], ] Hide Tags Backtracking 链接: http://leetcode.com/problems/combi…

77. Combinations(medium, backtrack, 重要, 弄了1小时)

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], ] 做了好几个这种题了,就是 backtrack problem, 1小时做出,但不容易,各种小毛病. 我的程序蠢蠢的建立了一个 vec…

【一天一道LeetCode】#77. Combinations

一天一道LeetCode 本系列文章已全部上传至我的github,地址:ZeeCoder's Github 欢迎大家关注我的新浪微博,我的新浪微博欢迎转载,转载请注明出处 (一)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]…

[leetcode]77. Combinations组合

Given two integers n and k, return all possible combinations of k numbers out of 1 ... n. Example: Input: n = 4, k = 2 Output: [ [2,4], [3,4], [2,3], [1,2], [1,3], [1,4], ] 题目…

77. Combinations (java 求C(n,k)的组合，排除重复元素)

题目: Given two integers n and k, return all possible combinations of k numbers out of 1 ... n. 解析:同求全部组合的过程一样,只是这里限制每个组合中元素的个数为k,求所有组合时并不限制元素个数. 若要排除重复的元素,则首先对所有元素进行排序. 代码: public static List<List<Integer>> getAllCombinations(int[] array,int k)…

（效率低下）77. Combinations C++回溯法组合

https://leetcode.com/problems/combinations/ 沿用78题的思路 class Solution { public: void backTrack(vector<int> ans, vector<int> nums, vector<vector<int>>& res, int times,int k) { if(ans.size() == k) { res.push_back(ans); } else { for…

LeetCode OJ 77. Combinations

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], ] 解答用递归,对i-n求k个数的组合,先确定一个数j(其中i <= j <= n + 1 - k),然后对(i + 1)-n…

LeetCode 77 Combinations(排列组合)

题目链接:https://leetcode.com/problems/combinations/#/description Problem:给两个正数分别为n和k,求出从1,2.......n这n个数字选择k个数字作为一个组合,求出所有的组合. 数学问题:排列组合问题,可以得到这样的组合个数为:C(n,k) 代码实现:递归程序实现. 从1开始遍历到n为止,中间使用tempList保存每一个组合,只有当这个tempList的长度等于k时,将这个tempList添加到ans中. …

77. Combinations(回溯)

Given two integers n and k, return all possible combinations of k numbers out of 1 ... n. Example: Input: n = 4, k = 2 Output: [ [2,4], [3,4], [2,3], [1,2], [1,3], [1,4], ] class Solution { List<List<Integer>> res = new ArrayList<>(); pu…

77. Combinations (Recursion)

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:遍历n以内的正整数,每个数有放入与不放入两种选择=>带回溯的递归 class Solution { public: vector…

【LeetCode】77. Combinations (2 solutions)

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], ] 解法一:递归递推点:加入i后,下一个加入的元素需要遍历i+1~n 因此可以基于k做递归. base cas…

leetCode 77.Combinations (组合)

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:此题意思是给一个n,和k,求1-n的k个数的组合.没有反复(位置交换算反复).可用排列组合的统一公式求解. 代码例如以下: p…

[LeetCode] 77. Combinations 全组合

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], ] 给两个数字n, k,返回所有由[1...n]中的k数字组合的可能解. 解法1: 递归解法2: 迭代 C++: Recursion c…

77. Combinations (JAVA)

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], ] 带回溯的递归.(带回溯没法用循环实现) class Solution { public List<List<Integer>&…

[LC] 77. Combinations

Given two integers n and k, return all possible combinations of k numbers out of 1 ... n. Example: Input: n = 4, k = 2 Output: [ [2,4], [3,4], [2,3], [1,2], [1,3], [1,4], ] Time: O(C(N, k)) class Solution: def combine(self, n: int, k: int) -> List[Li…

【LeetCode】77. Combinations 解题报告（Python & C++）

作者: 负雪明烛 id: fuxuemingzhu 个人博客: http://fuxuemingzhu.cn/ 目录题目描述题目大意解题方法方法一:递归方法二:回溯法日期题目地址:https://leetcode.com/problems/combinations/description/ 题目描述 Given two integers n and k, return all possible combinations of k numbers out of 1 - n. For…

[刷题] 77 Combinations

要求给出两个整数n和k,在n个数字中选出k个数字的所有组合示例 n=4 , k=2 [ [ 1, 2 ] , [ 1, 3 ] , [ 1, 4 ] , [ 2, 3 ] , [ 2, 4 ] , [ 3, 4 ] ] 思路实现 combine():求解C(n,k) generateCombinations():递归求解 res:二维向量,保存已经找到的组合 start:整型,开始搜索的位置 c:向量,已经找到的组合 1 class Solution { 2 3 private: 4 ve…

Permutations,Permutations II,Combinations

这是使用DFS来解数组类题的典型题目,像求子集,和为sum的k个数也是一个类型解题步骤: 1:有哪些起点,例如,数组中的每个元素都有可能作为起点,那么用个for循环就可以了. 2:是否允许重复组合 3:处理某个数,判断结果 4:dfs递归 5:还原现场一:Permutations Given a collection of numbers, return all possible permutations. For example,[1,2,3] have the following per…

LeetCode All in One 题目讲解汇总(持续更新中...)

终于将LeetCode的免费题刷完了,真是漫长的第一遍啊,估计很多题都忘的差不多了,这次开个题目汇总贴,并附上每道题目的解题连接,方便之后查阅吧~ 477 Total Hamming Distance 44.10% Meidum 475 Heaters 30.20% Easy 474 Ones and Zeroes 34.90% Meidum 473 Matchsticks to Square 31.80% Medium 472 Concatenated Words 29.20% Hard…

[leetcode] 题型整理之排列组合

一般用dfs来做最简单的一种: 17. Letter Combinations of a Phone Number Given a digit string, return all possible letter combinations that the number could represent. A mapping of digit to letters (just like on the telephone buttons) is given below. Input:Digit s…

leetcode bugfree note

463. Island Perimeterhttps://leetcode.com/problems/island-perimeter/就是逐一遍历所有的cell,用分离的cell总的的边数减去重叠的边的数目即可.在查找重叠的边的数目的时候有一点小技巧,就是沿着其中两个方向就好,这种题目都有类似的规律,就是可以沿着上三角或者下三角形的方向来做.一刷一次ac,但是还没开始注意codestyle的问题,需要再刷一遍. class Solution { public: int islandPerime…

LeetCode 刷题顺序表

Id Question Difficulty Frequency Data Structures Algorithms 1 Two Sum 2 5 array + set sort + two pointers 2 Add Two Numbers 3 4 linked list two pointers + math 3 Longest Substring Without Repeating Characters 3 2 string + hashtable two pointers 4 Med…