Description Computing the exact number of ways that N things can be taken M at a time can be a great challenge when N and/or M become very large. Challenges are the stuff of contests. Therefore, you are to make just such a computation given the follo…

最近编程时经常要用到排序组合的代码,想当年还抱着一些情况买了一本<组合数学>,不过现在这货也不知道被自己放哪里了,估计不会是垫桌子腿了吧. 由于去年去东北大学考博面试的时候遇到过可能涉及排列组合的编程题,要我当时很是十分的下不来台,所以现在遇到这货比较敏感,虽然用到的时候直接调用库就万事大吉,不过细细想来总觉不妥,遂把库函数的说明文档调了出来. https://docs.python.org/dev/library/itertools.html#itertools.combinations i…

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], ] 分析: 组合的实现,之前实现过全排列,递归求解 class Solution { public: vector<vector<int…

Numbers can be regarded as product of its factors. For example, 8 = 2 x 2 x 2; = 2 x 4. Write a function that takes an integer n and return all possible combinations of its factors. Note: Each combination's factors must be sorted ascending, for examp…

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], ] 这道题让求1到n共n个数字里k个数的组合数的所有情况,还是要用深度优先搜索DFS来解,根据以往的经验,像这种要求出所有结果的集合,一般…

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 string "23" Output: ["ad", "ae", &q…

Numbers can be regarded as product of its factors. For example, 8 = 2 x 2 x 2; = 2 x 4. Write a function that takes an integer n and return all possible combinations of its factors. Note: You may assume that n is always positive. Factors should be gr…

题目: 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 string "23" Output: ["ad", "ae"…

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 string "23" Output: ["ad", "ae", &…

https://leetcode.com/problems/combination-sum-ii/ 题目跟前面几道题很类似,直接写代码: class Solution { public: vector<vector<int>> combinationSum2(vector<int>& candidates, int target) { sort(candidates.begin(),candidates.end()); ) return res; vector&…

问题: 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.Example:Input:Digit string "23"Output: ["ad", "ae&…

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…

Factor Combinations Problem: Numbers can be regarded as product of its factors. For example, 8 = 2 x 2 x 2; = 2 x 4. Write a function that takes an integer n and return all possible combinations of its factors. Note: Each combination's factors must b…

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 string "23" Output: ["ad", "ae", &q…

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:有点像0-1背包问题, 对于从1-n的每一个数字都可以选择放入答案 和不放入答案. 当长度达到k时就是一个符合条件的解. 递归的…

题目链接 题意:有一排砖,可以染红蓝绿黄四种不同的颜色,要求红和绿两种颜色砖的个数都是偶数,问一共有多少种方案,结果对10007取余. 题解:刚看这道题第一感觉是组合数学,正向推了一会还没等推出来队友就打表找到公式了,然后我就写了一个快速幂加个费马小定理就过了去看别的题了,赛后找到了一个很不错的博客:传送门,原来这道题也可以用DP+矩阵快速幂AC.下面说下组合数学的做法: 首先一共有4^n种情况,我们减去不符合条件的情况就行了,从中取k个进行染红绿色一共C(n,k)种情况,剩下的蓝黄色一共有2^…

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 string "23" Output: ["ad", "ae", &q…

背包解组合数学问题,n种物品,每种num[i]个,求取r个的方法数. 背包思想,f[j]表示当前取j个数的方法数,则状态转移方程为 f[j] += f[k](max(j - num[i], 0) <= k < j) 外层循环枚举物品,内层循环从大到小枚举空间,最内层枚举方法数. #include<cstdio> #include<iostream> #include<cstdlib> #include<cstring> #include<s…

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. Notice Although the above answer is in lexicographical order, your answe…

原题链接在这里:https://leetcode.com/problems/factor-combinations/ 题目: Numbers can be regarded as product of its factors. For example, 8 = 2 x 2 x 2; = 2 x 4. Write a function that takes an integer n and return all possible combinations of its factors. Note:…

Learn about the startup key combinations you can use with Intel-based Macs. You can use the following startup key combinations with Intel-based Macs. Keystroke Description Press C during startup Start up from a bootable CD, DVD, or USB thumb drive (s…

Sort Colors Given an array with n objects colored red, white or blue, sort them so that objects of the same color are adjacent, with the colors in the order red, white and blue. Here, we will use the integers 0, 1, and 2 to represent the color red, w…

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 string "23" Outpu…

1 题目: 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 string "23" Output: ["ad", "ae&quo…

模板问题: 1. 取物品 (comb.pas/c/cpp) [问题描述] 现在有n个物品(有可能相同),请您编程计算从中取k个有多少种不同的取法.[输入] 输入文件有两行,第一行包含两个整数n,k(2<=n<=30,0<=k<=n).第二行,包含n个整数表示物品的编号(范围1..1000).编号相同的物品看作同一种物品. 想想看,组合数学中有这样的模型吗?答案是,肯定会有的.但是因为这个问题的灵活性,还没有通项公式. 想象当每个数都不同时,这个问题就变成了${n \choose k…

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 string "23" Outpu…

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], ] 解题思路: DFS,JAVA实现如下: public static void main(String args[]) { List<…

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. 解题思路: 思路一: 使用DFS算法,JAVA实现如下: static String[] alpha = new String[] { " &q…

题目传送门 /* 题意:求第K个全排列 组合数学:首先,使用next_permutation 函数会超时,思路应该转变, 摘抄网上的解法如下: 假设第一位是a,不论a是什么数,axxxxxxxx一共有8!种选择. 297192 div 8! = 7,余14952,所以第一位是1-9中的第8个数,也就是8. 14952 div 7! = 2,余4872,所以第二位是3. 4872 div 6! = 6,余552,所以是第三位是1245679这七个数中的第7个,也就是 9. 552 div 5! =…

这是Combinations 组合项 的延伸,在这里,我们允许不同的顺序出现,那么新的题目要求如下: 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: [ [1,2], [1,3], [1,4], [2,1], [2,3], [2,4], [3,1], [3,2], [3,4…