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q0528.swift
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q0528.swift
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//
// q0528.swift
// LeetcodeSwift
//
// Created by NowOrNever on 06/06/2020.
// Copyright © 2020 DL. All rights reserved.
//
import Foundation
//528. Random Pick with Weight
//Medium
//
//592
//
//1354
//
//Add to List
//
//Share
//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 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 w. pickIndex has no arguments. Arguments are always wrapped with a list, even if there aren't any.
//
//Accepted
//68,330
//Submissions
//156,043
class q0528Solution {
fileprivate var numbers = [Int]()
fileprivate var length = 0
init(_ w: [Int]) {
numbers.removeAll()
var number = 0
for item in w {
number += item
numbers.append(number)
}
length = number
}
func pickIndex() -> Int {
guard length > 0 else {
return 0
}
let number = Int.random(in: 1 ... length)
var left = 0
var right = numbers.count - 1
var result = 0
while left <= right {
let mid = (left + right) / 2
if numbers[mid] == number {
result = mid
break
}else if number < numbers[mid] {
right = mid - 1
}else if number > numbers[mid]{
result = mid
left = mid + 1
}
}
return result
}
}
/**
* Your Solution object will be instantiated and called as such:
* let obj = Solution(w)
* let ret_1: Int = obj.pickIndex()
*/