# 58.2 左旋转字符串

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## 题目描述

```html
Input:
S="abcXYZdef"
K=3

Output:
"XYZdefabc"
```

## 解题思路

先将 "abc" 和 "XYZdef" 分别翻转，得到 "cbafedZYX"，然后再把整个字符串翻转得到 "XYZdefabc"。

```java
public String LeftRotateString(String str, int n) {
    if (n >= str.length())
        return str;
    char[] chars = str.toCharArray();
    reverse(chars, 0, n - 1);
    reverse(chars, n, chars.length - 1);
    reverse(chars, 0, chars.length - 1);
    return new String(chars);
}

private void reverse(char[] chars, int i, int j) {
    while (i < j)
        swap(chars, i++, j--);
}

private void swap(char[] chars, int i, int j) {
    char t = chars[i];
    chars[i] = chars[j];
    chars[j] = t;
}
```






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