微软算法100题26 左旋转字符串

 1 package com.rui.microsoft;
 2 
 3 public class Test26_LeftRotateString {
 4 
 5     public static void main(String[] args) {
 6         String s = leftRotate("abcdef", 5);
 7         System.out.println(s);
 8     }
 9     
10     public static String leftRotate(String s, int from){
11         StringBuilder sb = new StringBuilder();
12         
13         //reverse all
14         s = reverse(s);
15         
16         String s0 = s.substring(0, s.length() - from + 1);
17         String s1 = s.substring(s.length() - from + 1, s.length());
18         
19         //reverse each part
20         sb.append(reverse(s0)).append(reverse(s1));
21         return sb.toString();
22     }
23     
24     private static String reverse(String s){
25         char[] as = s.toCharArray();
26         int i = 0;
27         int j = s.length() - 1;
28         while(i<j){
29             swap(as, i,j);
30             i++;
31             j--;
32         }
33         return String.copyValueOf(as);
34     }
35     
36     private static void swap(char[] a, int i, int j){
37         char temp = a[i];
38         a[i] = a[j];
39         a[j] = temp;
40     }
41 }