字符串旋转检测算法

题目：

Assume you have a method isSubstring which checks if one word is a substring of another. 

Given two strings, s1 and s2, write code to check if s2 is a rotation of s1 using only one call to isSubstring

 (i.e., “waterbottle” is a rotation of “erbottlewat”).

解决思路：

1. Check if length(s1) == length(s2). If not, return false.
2. Else, concatenate s1 with itself and see whether s2 is substring of the result.

• input: s1 = apple, s2 = pleap ==> apple is a substring of pleappleap
• input: s1 = apple, s2 = ppale ==> apple is not a substring of ppaleppale

源码如下：

#include <iostream>#include <string>using namespace std;bool isSubstring(string s1, string s2){    if(s1.find(s2) != string::npos) return true;    else return false;}bool isRotation(string s1, string s2){    if(s1.length() != s2.length() || s1.length()<=0)        return false;    return isSubstring(s1+s1, s2);}int main(){    string s1 = "apple";    string s2 = "pleap";    cout<<isRotation(s1, s2)<<endl;    cout<<string::npos<<endl;    return 0;}