Question 398. Random Pick Index Solution 思路:重点是如果数据中有多个数target相等,要从这些数中随机取一个,根据例题 假设输入是: int[] nums = new int[]{1, 2, 3, 3, 3}; int target = 3; 模拟: 1 != target pass 2 != target pass 3 == target pick的概率 nextInt(1)==0的概率 1,返回这个index的概念是1 - 1/3 -1/3 = 1…

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 每次遍历索引 字典保存索引 蓄水池抽样 日期 题目地址:https://leetcode.com/problems/random-pick-index/description/ 题目描述 Given an array of integers with possible duplicates, randomly output the index of…

Given an array of integers with possible duplicates, randomly output the index of a given target number. You can assume that the given target number must exist in the array. Note: The array size can be very large. Solution that uses too much extra sp…

我是链接 看到这道题,想到做的几道什么洗牌的题,感觉自己不是很熟,但也就是rand()函数的调用,刚开始用map<int, vector<int >>来做,tle,后来就想着直接保存nums数组,和每个元素的数目,然后先生成一个随机的第几个target,然后从nums里面再找这个index,交了,就过了,有套路么? class Solution { public: map<int, int> m; vector<int> num; Solution(vect…

随机返还target值的坐标(如果存在多个target). 不太明白为什么这个题是M难度的. 无非是要么弄TABLE之类的,开始麻烦点,但是pick的时候直接PICK出来就行了. 要么开始简单点,都存了,选的时候再随机选. 前者各种溢出..貌似memory在leetcode比较值钱..就用后者 public class Solution { int[] nums; public Solution(int[] nums) { this.nums = nums; } public int pick(…

［抄题］: Given an array of integers with possible duplicates, randomly output the index of a given target number. You can assume that the given target number must exist in the array. Note:The array size can be very large. Solution that uses too much ext…

Given an array of integers with possible duplicates, randomly output the index of a given target number. You can assume that the given target number must exist in the array. Note:The array size can be very large. Solution that uses too much extra spa…

给定一个可能含有重复元素的整数数组,要求随机输出给定的数字的索引. 您可以假设给定的数字一定存在于数组中.注意:数组大小可能非常大. 使用太多额外空间的解决方案将不会通过测试.示例:int[] nums = new int[] {1,2,3,3,3};Solution solution = new Solution(nums);// pick(3) 应该返回索引 2,3 或者 4.每个索引的返回概率应该相等.solution.pick(3);// pick(1) 应该返回 0.因为只有nums[…

Given an array of integers with possible duplicates, randomly output the index of a given target number. You can assume that the given target number must exist in the array. Note: The array size can be very large. Solution that uses too much extra sp…

Given an array of integers with possible duplicates, randomly output the index of a given target number. You can assume that the given target number must exist in the array. Note: The array size can be very large. Solution that uses too much extra sp…

Given an array of integers with possible duplicates, randomly output the index of a given target number. You can assume that the given target number must exist in the array. Note:The array size can be very large. Solution that uses too much extra spa…

Given an array of integers with possible duplicates, randomly output the index of a given target number. You can assume that the given target number must exist in the array. Note:The array size can be very large. Solution that uses too much extra spa…

Given a blacklist B containing unique integers from [0, N), write a function to return a uniform random integer from [0, N) which is NOT in B. Optimize it such that it minimizes the call to system’s Math.random(). Note: 1 <= N <= 1000000000 0 <=…

Given an array w of positive integers, where w[i] describes the weight of index i, write a function pickIndex which randomly picks an index in proportion to its weight. Note: 1 <= w.length <= 10000 1 <= w[i] <= 10^5 pickIndex will be called at…

原题链接在这里:https://leetcode.com/problems/random-pick-with-weight/ 题目: Given an array w of positive integers, where w[i] describes the weight of index i, write a function pickIndex which randomly picks an index in proportion to its weight. Note: 1 <= w.l…

Question 710. Random Pick with Blacklist Solution 题目大意:给一个N,表示一个范围[0,N),给一个黑名单列表blacklist,其中blacklist中的元素在[0,N)范围内,调用pick方法的时候随机返回一个数,这个数满足 在[0,N)范围 不在blacklist内 要随机 思路:构造一个集合M,该M是 [0,N) - blacklist 的一个集合,调用pick时,返回[0,M)的一个随机数并根据这个随机数从集合M中取数即可. Java实…

作者: 负雪明烛 id: fuxuemingzhu 个人博客: http://fuxuemingzhu.cn/ 题目地址:https://leetcode.com/problems/random-pick-with-weight/description/ 题目描述: Given an array w of positive integers, where w[i] describes the weight of index i, write a function pickIndex which…

［抄题］: Given an array w of positive integers, where w[i] describes the weight of index i, write a function pickIndex which randomly picks an index in proportion to its weight. Note: 1 <= w.length <= 10000 1 <= w[i] <= 10^5 pickIndex will be cal…

Given an array w of positive integers, where w[i] describes the weight of index i, write a function pickIndex which randomly picks an index in proportion to its weight. Note: 1 <= w.length <= 10000 1 <= w[i] <= 10^5 pickIndex will be called at…

Given an array w of positive integers, where w[i] describes the weight of index i, write a function pickIndex which randomly picks an index in proportion to its weight. Note: 1 <= w.length <= 10000 1 <= w[i] <= 10^5 pickIndex will be called at…

Given a blacklist B containing unique integers from [0, N), write a function to return a uniform random integer from [0, N) which is NOT in B. Optimize it such that it minimizes the call to system’s Math.random(). Note: 1 <= N <= 1000000000 0 <=…

1. 问题 给定一个黑名单,包含[0, N)的一些数,从[0, N)之间的非黑名单数中随机采样一个值. 2. 思路 字典映射 (1)计算黑名单数的长度,记作B,因为已经排除掉了B个元素,所以最后是从N-B个数中采样. (2)可以维护一个字典,表示从[0, N-B)到[0, N)之间的映射. (3)这样就可以每次采样从[0, N-B)之间取,采样后将值映射回[0, N). (4)然而这么做爆内存了(MemoryError),因为N的最大长度为10亿,B的最大长度为10万,N-B特别大. 时间复杂度…

Given an array w of positive integers, where w[i] describes the weight of index i, write a function pickIndex which randomly picks an index in proportion to its weight. class Solution { Random random; int[] wSums; public Solution(int[] w) { this.rand…

1. 问题 给定一个权重数组w,w[i]表示下标i的权重,根据权重从数组中随机抽取下标. 2. 思路 这道题相当于 497. Random Point in Non-overlapping Rectangles的一个简化版. (1)可以先依次对每个下标的权重累加存起来(相当于概率分布中的分布累积函数CDF,Cumulative Distribution Function). (2)从 [1, 总权重] 中随机取一个数n,根据这个数在多个累加权重之间寻找合适的位置,即可完成题目要求的随机采样. (…

题目描述 给定一个 32 位有符号整数,将整数中的数字进行反转. 示例 1: 输入: 123 输出: 321  示例 2: 输入: -123 输出: -321 示例 3: 输入: 120 输出: 21 注意: 假设我们的环境只能存储 32 位有符号整数,其数值范围是 [−231,  231 − 1].根据这个假设,如果反转后的整数溢出,则返回 0. 解题思路 反转整数的思路是从一个数的最后一位开始,依次向前遍历,每次反转整数依次左移一位,并取出一位数作为新数的末位数.具体而言首先定义反转以后的数…

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 数组保存再随机选择 蓄水池抽样 日期 题目地址:https://leetcode.com/problems/linked-list-random-node/description/ 题目描述 Given a singly linked list, return a random node's value from the linked list. E…

384. Shuffle an Array random.nextInt(n) 返回[0, n) 的随机数,故要+1: class Solution { private int[] nums; private Random random; public Solution(int[] nums) { this.nums = nums; random = new Random(); } /** Resets the array to its original configuration and re…

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…

刷题备忘录,for bug-free leetcode 396. Rotate Function 题意: Given an array of integers A and let n to be its length. Assume Bk to be an array obtained by rotating the array A k positions clock-wise, we define a "rotation function" F on A as follow: F(k…

刷题备忘录,for bug-free 招行面试题--求无序数组最长连续序列的长度,这里连续指的是值连续--间隔为1,并不是数值的位置连续 问题: 给出一个未排序的整数数组,找出最长的连续元素序列的长度. 如: 给出[100, 4, 200, 1, 3, 2], 最长的连续元素序列是[1, 2, 3, 4].返回它的长度:4. 你的算法必须有O(n)的时间复杂度 . 解法: 初始思路 要找连续的元素,第一反应一般是先把数组排序.但悲剧的是题目中明确要求了O(n)的时间复杂度,要做一次排序,是不能达…