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. 1 <= w.length <= 10000
  2. 1 <= w[i] <= 10^5
  3. pickIndex will be called at most 10000 times.

Example 1:

Input:
["Solution","pickIndex"]
[[[1]],[]]
Output: [null,0]

Example 2:

Input:
["Solution","pickIndex","pickIndex","pickIndex","pickIndex","pickIndex"]
[[[1,3]],[],[],[],[],[]]
Output: [null,0,1,1,1,0]

Explanation of Input Syntax:

The input is two lists: the subroutines called and their arguments. Solution's constructor has one argument, the array wpickIndex has no arguments. Arguments are always wrapped with a list, even if there aren't any.

题解:

The given input array means for current index i, the weight is w[i].

e.g. w = [20, 20, 60]. The weight of choosing 0 is 20, the weight of choosing 1 is 20, the weight of choosing 2 is 60, totally it is 100.

In order to choose by weight, we need to accumlat the total weight, and pick a random number within [1, total weight].

sum = [20, 40, 100]

And binary search where this weight would land.

If sum[mid] == pick, then simply return mid.

Else if sum[mid] < pick, say pick = 50, sum[mid] = 40, then it can't be index 1, since 1 is from 20 to 40. l = mid + 1.

Else if sum[mid] > pick, say pick = 30, sum[mid] = 40, then it could still be index 1, since 1 is from 20 to 40. r = mid.

When using above transion, while loop condision is l < r, it can't be l <= r. Otherwise, it would get out of loop.

Time Complexity: pickIndex, O(logw.length).

Space: O(1). It doesn't have extra array, it is changing input w array.

AC Java:

 class Solution {
int [] sum;
Random rand; public Solution(int[] w) {
for(int i = 1; i<w.length; i++){
w[i] += w[i-1];
} this.sum = w;
this.rand = new Random();
} public int pickIndex() {
int len = sum.length;
int n = sum[len-1];
int pick = rand.nextInt(n) + 1; int l = 0;
int r = len-1;
while(l < r){
int mid = l + (r - l) / 2;
if(sum[mid] == pick){
return mid;
}else if(sum[mid] < pick){
l = mid + 1;
}else{
r = mid;
}
} return l;
}
} /**
* Your Solution object will be instantiated and called as such:
* Solution obj = new Solution(w);
* int param_1 = obj.pickIndex();
*/

类似Random Pick IndexLinked List Random Node.

LeetCode 528. Random Pick with Weight的更多相关文章

  1. [leetcode]528. Random Pick with Weight按权重挑选索引

    Given an array w of positive integers, where w[i] describes the weight of index i, write a function  ...

  2. 【LeetCode】528. Random Pick with Weight 解题报告(Python)

    作者: 负雪明烛 id: fuxuemingzhu 个人博客: http://fuxuemingzhu.cn/ 题目地址:https://leetcode.com/problems/random-pi ...

  3. 528. Random Pick with Weight index的随机发生器

    [抄题]: Given an array w of positive integers, where w[i] describes the weight of index i, write a fun ...

  4. 528. Random Pick with Weight

    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 Recta ...

  5. [LeetCode] Random Pick with Weight 根据权重随机取点

    Given an array w of positive integers, where w[i] describes the weight of index i, write a function  ...

  6. [Swift]LeetCode528. 按权重随机选择 | Random Pick with Weight

    Given an array w of positive integers, where w[i] describes the weight of index i, write a function  ...

  7. [LeetCode] 398. Random Pick Index ☆☆☆

    Given an array of integers with possible duplicates, randomly output the index of a given target num ...

  8. Random Pick with Weight

    Given an array w of positive integers, where w[i] describes the weight of index i, write a function  ...

  9. [leetcode] 398. Random Pick Index

    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 ...

随机推荐

  1. Laravel自定义排序

    如果数据库的status字段有0,1,2,3几种状态,如果想让status为1,2的状态排在最前面 那么可以这样: $obj = $obj->orderByRaw(DB::raw('FIELD( ...

  2. 发送邮件报错javax.activation.UnsupportedDataTypeException: no object DCH for MIME type multipart/mixed

    关于使用javaMail发送邮件报错:javax.activation.UnsupportedDataTypeException: no object DCH for MIME type multip ...

  3. SpringMVC-方法四种类型返回值总结,你用过几种?

    SpringMVC 现在算是 Java 领域的一个基础性框架了,很多人天天用,可是对于 SpringMVC 方法的返回值,你又是否完全清楚呢?今天松哥就来和大家聊一聊 SpringMVC 中四种不同类 ...

  4. 2019-11-29-WPF-多个-StylusPlugIn-的事件触发顺序

    原文:2019-11-29-WPF-多个-StylusPlugIn-的事件触发顺序 title author date CreateTime categories WPF 多个 StylusPlugI ...

  5. 2019-11-29-WPF-绑定命令在-MVVM-的-CanExecute-和-Execute-在按钮点击都没触发可能的原因...

    原文:2019-11-29-WPF-绑定命令在-MVVM-的-CanExecute-和-Execute-在按钮点击都没触发可能的原因... title author date CreateTime c ...

  6. 类初始化应用(class初始化值用函数改变与增添)

    class Dataset(object): def __init__(self): self.image_info = [] # 初始化一个列表 def add_image(self, source ...

  7. Windows Server2008R2,ServerWin2012 R2设置自动登录注册表配置

    serverWin2008 R2 2012自动登录一般是通过control userpasswords2 命令修改,其实注册表修改更简单.复制以下保存为xx.reg文件导入即可即可. Windows ...

  8. Spring Cloud微服务架构升级总结

    ↵ [编者的话]微服务的概念源于 2014 年 3 月 Martin Fowler 所写的一篇文章“Microservices”.文中内容提到:微服务架构是一种架构模式,它提倡将单一应用程序划分成一组 ...

  9. Windows下VS Code打开黑屏解决办法(这样真的行)

    版权声明:本文为博主原创文章,遵循 CC 4.0 BY-SA 版权协议,转载请附上原文出处链接和本声明.本文链接:https://blog.csdn.net/qq_42421611/article/d ...

  10. vue-cli随机生成port源码

    const portfinder = require('portfinder'): const port = await portfinder.getPortPromise(): 两行代码 端口搜索范 ...