在 Swift 中避免使用 arc4random 重复

Question

我有以下代码在 Swift 中生成随机填充的网格：

import Foundation

var tile = [String](count: 900, repeatedValue: ".")

// Randomly populate the grid with hashes
for i in 0...400 {
    tile[Int(arc4random_uniform(899))] = "#"
}

// Print the grid to console
for y in 0...(29) {
    for x in 0...(29) {
        print("\(tile[y * 10 + x])")
    }
    println("")
}

运行此代码生成如下所示的网格：

..##..#.#...#..#..#.#.####.#..
..#..#..#.#.####.#....###.#.#.
#.####.#....###.#.#.#####.....
..###.#.#.#####.....#...#....#
#####.....#...#....###.##.###.
#...#....###.##.###..#.....#..
##.##.###..#.....#...##..#.##.
.#.....#...##..#.##...#.####..
.##..#.##...#.####..###..#.#.#
..#.####..###..#.#.#.#..#.....
###..#.#.#.#..#.........#...##
.#..#.........#...##.##.......
....#...##.##............#...#
.##............#...####....##.
.....#...####....##..#.#.....#
###....##..#.#.....#........#.
.#.#.....#........#...#.#..#..
........#...#.#..#......#....#
..#.#..#......#....#.##.#...##
....#....#.##.#...###...#..#..
.##.#...###...#..#..#.#..#...#
#...#..#..#.#..#...#####...##.
#.#..#...#####...##..#.......#
####...##..#.......#.#.#.....#
.#.......#.#.#.....##.........
.#.#.....##..........##.#..#.#
#..........##.#..#.##.#.#.....
.##.#..#.##.#.#.....##...#....
#.#.#.....##...#......#.##....
##...#......#.##.....#.######.

你可以清楚地看到一个模式在重复。有没有办法让"throw"功能让生成更有说服力？

Answer 1

你的打印函数是错误的：tile[y*10 + x]应该是tile[y*30 + x]。

至于生成网格：您到底想要什么？

如果答案是"a random choice from the uniform distribution over the space of all possible 30x30 grids, where each cell is either # or ."，那么您应该简单地选择具有#和.:

等概率的每个单元格

for i in 0..<900 {
    // arc4random_uniform(2) is either 0 or 1, with equal probability
    tile.append(arc4random_uniform(2) == 0 ? "." : "#")
}

如果答案是"a random choice from the uniform distribution over 30x30 grids in which exactly 400 cells are #"，那么你应该预先选择400个唯一索引，然后再将它们转换为#。

照原样，您的代码可能生成只有一个 # 的网格（尽管这种可能性很小）。而且它 永远不会 生成超过 400 # 的网格。

Answer 2

您只将 900 个中的 400 个转换为 #
您将有很多重复项（用# 覆盖#），所以我希望有很多“.”。剩下的。

我觉得你显示的模式还不错。

把你所有的货物都放在bag/array里，随机分类，然后一件一件拉出来。

在 Swift 中避免使用 arc4random 重复

Avoiding repetition with arc4random in Swift

swift

random

arc4random