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”) 

這道題沒想到這麼做，很巧妙

#include <iostream>
using namespace std;

bool isSubstring(char* src, char* tar)
{
    return strstr(src, tar)!=NULL;
};

bool isRotation(char* src, char* tar)
{
    int len = strlen(src);
    if(len != strlen(tar))
        return false;
    char* newSrc = new char[len * 2 + 1];
    strcpy(newSrc, src);
    strcpy(newSrc+len, src);
    return isSubstring(newSrc, tar);
};

int main()
{
    cout<<boolalpha<<isRotation("a1bd12fswfd", "a1bd12fswfd");
    system("pause"); 
};