```
#include<iostream>
#include<cstring>
using namespace std;
// A utility function to fill lps[] or compute prefix function
// used in KMP string matching algorithm.
void computeLPSArray(char str[], int M, int lps[])
{
int len = 0; //lenght of the previous longest prefix suffix
int i;
lps[0] = 0; //lps[0] is always 0
i = 1;
// the loop calculates lps[i] for i = 1 to M-1
while (i < M)
{
if (str[i] == str[len])
{
len++;
lps[i] = len;
i++;
}
else // (pat[i] != pat[len])
{
if (len != 0)
{
// This is tricky. Consider the example AAACAAAA
// and i = 7.
len = lps[len-1];
// Also, note that we do not increment i here
}
else // if (len == 0)
{
lps[i] = 0;
i++;
}
}
}
}
// Returns true if str is repetition of one of its substrings
// else return false.
bool isRepeat(char str[])
{
// Find length of string and create an array to
// store lps values used in KMP
int n = strlen(str);
int *lps;
lps = (int *)malloc(n*sizeof(int));
// Preprocess the pattern (calculate lps[] array)
computeLPSArray(str, n, lps);
// Find length of longest suffix which is also
// prefix of str.
int len = lps[n-1];
// If there exist a suffix which is also prefix AND
// Length of the remaining substring divides total
// length, then str[0..n-len-1] is the substring that
// repeats n/(n-len) times (Readers can print substring
// and value of n/(n-len) for more clarity.
return (len > 0 && n%(n-len) == 0)? true: false;
}
// Driver program to test above function
int main()
{
char txt[][100] = {"ABCABC", "ABABAB", "ABCDABCD", "QUERYHOME", "AAAACAAAAC", "ABCDABC"};
int n = sizeof(txt)/sizeof(txt[0]);
for (int i=0; i<n; i++)
isRepeat(txt[i])? cout << "True\n" : cout << "False\n";
return 0;
}
```

Credit: http://www.geeksforgeeks.org/find-given-string-can-represented-substring-iterating-substring-n-times/