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;
}