# Kotlin 程序：使用递归来反转句子

> 原文： [https://www.programiz.com/kotlin-programming/examples/reverse-sentence](https://www.programiz.com/kotlin-programming/examples/reverse-sentence)

#### 在此程序中，您将学习在 Kotlin 中使用递归循环来反转给定的句子。

## 示例：使用递归反转句子

```kt
fun main(args: Array<String>) {
    val sentence = "Go work"
    val reversed = reverse(sentence)
    println("The reversed sentence is: $reversed")
}

fun reverse(sentence: String): String {
    if (sentence.isEmpty())
        return sentence

    return reverse(sentence.substring(1)) + sentence[0]
}
```

运行该程序时，输出为：

```kt
The reversed sentence is: krow oG
```

在上面的程序中，我们有一个递归函数`reverse()`。

在每次迭代中，我们使用`charAt(0)`将下一个`reverse()`函数的结果添加（连接）到句子的第一个字符。

递归调用必须在`charAt()`之前，因为这样最后一个字符将开始添加到左侧。 如果您颠倒顺序，您将得到原始句子。

最后，我们以空的`sentence`和`reverse()`返回相反的句子结束。

Execution steps

| 迭代 | `reverse()` | `substring()` | `reversedString` |
| --- | --- | --- | --- |
| 1 | `reverse("Go work")` | `"o Work"` | `result + "G"` |
| 2 | `reverse("o Work")` | `" Work"` | `result + "o" + "G"` |
| 3 | `reverse(" Work")` | `"Work"` | `result + " " + "o" + "G"` |
| 4 | `reverse("Work")` | `"ork"` | `result + "W" + " " + "o" + "G"` |
| 5 | `reverse("ork")` | `"rk"` | `result + "o" + "W" + " " + "o" + "G"` |
| 6 | `reverse("rk")` | `"k"` | `result + "r" + "o" + "W" + " " + "o" + "G"` |
| 7 | `reverse("k")` | `""` | `result + "k" + "r" + "o" + "W" + " " + "o" + "G"` |
| 最后 | `reverse("")` | - | `"" + "k" + "r" + "o" + "W" + " " + "o" + "G" = "kroW oG"` |

以下是等效的 Java 代码：[用来反转句子的 Java 程序](/java-programming/examples/reverse-sentence "Java Program to reverse a sentence")