[Swift]LeetCode710. 黑名单中的随机数 | Random Pick with Blacklist

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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. 1 <= N <= 1000000000
2. 0 <= B.length < min(100000, N)
3. [0, N) does NOT include N. See interval notation.

Example 1:

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

Example 2:

Input: 
["Solution","pick","pick","pick"]
[[2,[]],[],[],[]]
Output: [null,1,1,1]

Example 3:

Input: 
["Solution","pick","pick","pick"]
[[3,[1]],[],[],[]]
Output: [null,0,0,2]

Example 4:

Input: 
["Solution","pick","pick","pick"]
[[4,[2]],[],[],[]]
Output: [null,1,3,1]

Explanation of Input Syntax:

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

---

给定一个包含 [0，n ) 中独特的整数的黑名单 B，写一个函数从 [ 0，n ) 中返回一个不在 B 中的随机整数。

对它进行优化使其尽量少调用系统方法 Math.random() 。

提示:

1. 1 <= N <= 1000000000
2. 0 <= B.length < min(100000, N)
3. [0, N) 不包含 N，详细参见 interval notation 。

示例 1:

输入: 
["Solution","pick","pick","pick"]
[[1,[]],[],[],[]]
输出: [null,0,0,0]

示例 2:

输入: 
["Solution","pick","pick","pick"]
[[2,[]],[],[],[]]
输出: [null,1,1,1]

示例 3:

输入: 
["Solution","pick","pick","pick"]
[[3,[1]],[],[],[]]
Output: [null,0,0,2]

示例 4:

输入: 
["Solution","pick","pick","pick"]
[[4,[2]],[],[],[]]
输出: [null,1,3,1]

输入语法说明：

输入是两个列表：调用成员函数名和调用的参数。Solution的构造函数有两个参数，N 和黑名单 B。pick 没有参数，输入参数是一个列表，即使参数为空，也会输入一个 [] 空列表。

---

Runtime: 984 ms

Memory Usage: 23.4 MB

class Solution {
    var M:Int = 0
    var map:[Int:Int] = [Int:Int]()
    init(_ N: Int, _ blacklist: [Int]) {
        var N = N
        for b in blacklist
        {
            map[b] = -1
        }
        M = N - map.count
        for b in blacklist
        {
            if b < M
            {
                while (map[N - 1] != nil)
                {
                    N -= 1
                }
                map[b] = N - 1
                N -= 1
            }
        }        
    }
    
    func pick() -> Int {
        var p:Int = Int.random(in:0..<M)
        return map[p] == nil ? p : map[p]!      
    }
}

/**
 * Your Solution object will be instantiated and called as such:
 * let obj = Solution(N, blacklist)
 * let ret_1: Int = obj.pick()
 */ 

---

1628ms

class Solution {

    init(_ N: Int, _ blacklist: [Int]) {
        M = N - blacklist.count
        for n in blacklist {
            mapping[n] = 0
        }
        
        var i = M
        for n in blacklist {
            if n < M {
                while mapping[i] != nil {
                    i += 1
                }
                mapping[n] = i
                i += 1
            }
        }
    }
    
    func pick() -> Int {
        let r = Int.random(in: 0..<M)
        if let n = mapping[r] {
            return n
        }
        return r
    }
    
    var M : Int
    var mapping = [Int: Int]()
}

/**
 * Your Solution object will be instantiated and called as such:
 * let obj = Solution(N, blacklist)
 * let ret_1: Int = obj.pick()
 */