如何快速在字符串的最后三行之前添加一个新单词？答案

【问题标题】：How can I add a new word before last three lines in a string in swift?如何快速在字符串的最后三行之前添加一个新单词？
【发布时间】：2019-06-13 11:50:23
【问题描述】：

如何快速在字符串的最后三行之前添加一个新单词，以便该字符串可以从此转换：

"Who composed the\n
popular song "Aati Kya\n
Khandala" from 'Ghulam"?\n
Jatin- Lalit\n
Abhijeet\n
Aamir Khan"

到这里：

"Who composed the\n
popular song "Aati Kya\n
Khandala" from 'Ghulam"?\n
sagarduhanishere\n
Jatin- Lalit\n
Abhijeet\n
Aamir Khan"

【问题讨论】：

使用components(separatedBy:) 将String 转换为Array，然后在需要的地方插入新字符串，再将其转换回String？
你能给我写代码吗？

标签： swift algorithm slice

【解决方案1】：

这是正则表达式的方式。这是另一种选择。

        let s = """
        Who composed the
        popular song "Aati Kya
        Khandala" from 'Ghulam"?
        Jatin- Lalit
        Abhijeet
        Aamir Khan
        """

        let replaceString = "sagarduhanishere"

        let nextS = s.replacingOccurrences(of: "(\n.*){3}$", with: "\n\(replaceString)$0", options: .regularExpression  , range: nil)

        print(nextS)

【讨论】：

【解决方案2】：

接受的答案适用于短字符串。为了获得更好的空间（和时间）复杂性，您可以避免不必要地拆分字符串并重新加入数组的所有元素，这种方式：

让我们从这段文字开始：

let text = """
Who composed the
popular song "Aati Kya
Khandala" from 'Ghulam"?
Jatin- Lalit
Abhijeet
Aamir Khan
"""

结果将存储在这个变量中：

var result = ""

使用下面的代码，我们从原始字符串的末尾开始寻找第三个\n：

let start = text.startIndex
let end = text.endIndex
var index = text.index(end, offsetBy: -1)
var linesToGo = 3

while start < index  {
    if text[index] == "\n" {
        linesToGo -= 1
    }
    if linesToGo == 0 {
        index = text.index(index, offsetBy: 1)
        result = text[start..<index] + "sagarduhanishere\n" + text[index..<end]
        break
    }
    index = text.index(index, offsetBy: -1)
}

然后我们可以检查是否找到了 3 行

if linesToGo != 0 {
    fatalError("More lines needed")
}

然后打印结果或在您的代码中使用它：

print(result)

哪个输出：

Who composed the
popular song "Aati Kya
Khandala" from 'Ghulam"?
sagarduhanishere
Jatin- Lalit
Abhijeet
Aamir Khan

【讨论】：

【解决方案3】：

我想你有这样的字符串

let string = """
    "Who composed the
    popular song "Aati Kya
    Khandala" from 'Ghulam"?
    Jatin- Lalit
    Abhijeet
    Aamir Khan"
"""

或者像这样

let string = """
    "Who composed the\npopular song "Aati Kya\nKhandala" from 'Ghulam"?\nJatin- Lalit\nAbhijeet\nAamir Khan"
"""

所以，首先将你的字符串分隔成一个字符串数组

var separated = string.components(separatedBy: "\n")

然后在需要的索引处插入新字符串

separated.insert("sagarduhanishere", at: separated.endIndex - 3)

然后将这个数组加入到一个字符串中

let joined = separated.joined(separator: "\n")

var separated = string.components(separatedBy: "\n")
separated.insert("sagarduhanishere", at: separated.endIndex - 3)
let joined = separated.joined(separator: "\n")
print(joined)

"Who composed the popular song "Aati Kya Khandala" from 'Ghulam"? sagarduhanishere Jatin- Lalit Abhijeet Aamir Khan"

【讨论】：