【剑指Offer】58.2 左旋转字符串

Input:
S="abcXYZdef"
K=3

Output:
"XYZdefabc"

public class Solution {
    public String LeftRotateString(String str,int n) {
        if(str == null || str.length() == 0)
            return "";
        return str.substring(n, str.length()) + str.substring(0, n);
    }
}

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;
}