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LeftRotateString.java

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package _58;

public class LeftRotateString {

/**

* 实现一个函数完成字符串的左旋转功能。比如，输入 abcdefg 和数字 2，输出为 cdefgab。

*/

public static String leftRotateString(String str, int k) {

int n = str.length();

k = k % n;

if (k == 0) {

return str;

}

StringBuilder sb = new StringBuilder(str);

reverse(sb, 0, k - 1);

reverse(sb, k, n - 1);

reverse(sb, 0, n - 1);

return sb.toString();

}

public static void reverse(StringBuilder sb, int start, int end) {

for(int i = start; i <= start + (end - start)/2; i++) {

char temp = sb.charAt(i);

sb.setCharAt(i, sb.charAt(end - i + start));

sb.setCharAt(end - i + start, temp);

}

}

public static void main(String[] args) {

System.out.println(leftRotateString("abcdefg", 2));

}

}