面试任务.我们将如何解决呢? [英] Task from the interview. How we would solve it?

问题描述

以这种方式转换字符串

let initialString = "atttbcdddd"
// result must be like this "at3bcd4"

但是重复必须大于2.例如，如果我们有"aa"，结果将是"aa"，但是如果有"aaa"，结果将是"a3"

But repetition must be more than 2. For example, if we have "aa" the result will be "aa", but if we have "aaa", the result will be "a3"

另一个例子:

let str = "aahhhgggg"
//result "aah3g4"

我的尝试:

func encrypt(_ str: String) -> String {

    let char = str.components(separatedBy: "t") //must input the character
    var count = char.count - 1
    var string = ""
    string.append("t\(count)")
    return string
}

如果我输入"ttttt"，它将返回"t5"，但我应该输入字符

if i input "ttttt" it will return "t5" but i should input the character

推荐答案

您正在寻找的是游程编码" .请注意，这不是 加密！

What you are looking for is the "Run-length encoding". Note that this is not an encryption!

这是一个可能的实现(内嵌说明):

Here is a possible implementation (explanations inline):

func runLengthEncode(_ str: String) -> String {
    var result = ""
    var pos = str.startIndex // Start index of current run
    while pos != str.endIndex {
        let char = str[pos]
        // Find index of next run (or `endIndex` if there is none):
        let next = str[pos...].firstIndex(where: { $0 != char }) ?? str.endIndex
        // Compute the length of the current run:
        let length = str.distance(from: pos, to: next)
        // Append compressed output to the result:
        result.append(length <= 2 ? String(repeating: char, count: length) : "\(char)\(length)")
        pos = next // ... and continue with next run
    }
    return result
}

示例:

print(runLengthEncode("atttbcdddd")) // at3bcd4
print(runLengthEncode("aahhhgggg"))  // aah3g4
print(runLengthEncode("abbbaaa"))    // ab3a3

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