剑指 Offer 58 - II. 左旋转字符串

 1 class Solution {
 2 public:
 3     void reverse(string& s, int start, int end) { //翻转，区间写法：左闭右闭 []
 4         for (int i = start, j = end; i < j; i++, j--) {
 5             swap(s[i], s[j]);
 6         }
 7     }
 8     string reverseLeftWords(string s, int n) {
 9         if ((int)s.size() <= n) return s;
10         string front, last;
11         front.assign(s, 0, n);
12         last.assign(s, n , s.size() - n);
13         s = last + front;
14         return s;
15     }
16     string reverseLeftWords1(string s, int n) {
17        //先反转整个字符串，在分别反转前 size-n 个和后 n 个 
18         if ((int)s.size() <= n) return s;
19         reverse(s, 0, s.size() - 1);
20         reverse(s, 0, s.size() - n - 1);
21         reverse(s, s.size() - n, s.size() - 1);
22         return s;
23     }
24 };