Find minimum shift for longest common prefix

// CPP program to find longest common prefix
// after rotation of second string.
#include <bits/stdc++.h>
using namespace std;

// function for KMP search
void KMP(int m, int n, string str2, string str1)
{
	int pos = 0, len = 0;

	// preprocessing of longest proper prefix
	int p[m + 1];
	int k = 0;
	p[1] = 0;

	for (int i = 2; i <= n; i++) {
		while (k > 0 && str1[k] != str1[i - 1])
			k = p[k];
		if (str1[k] == str1[i - 1])
			++k;
		p[i] = k;
	}

	// find out the longest prefix and position
	for (int j = 0, i = 0; i < m; i++) {
		while (j > 0 && str1[j] != str2[i])
			j = p[j];
		if (str1[j] == str2[i])
			j++;

		// for new position with longer prefix in str2
		// update pos and len
		if (j > len) {
			len = j;
			pos = i - j + 1;
		}
	}

	// print result
	cout << "Shift = " << pos << endl;
	cout << "Prefix = " << str1.substr(0, len);
}

// driver function
int main()
{
	string str1 = "geeksforgeeks";
	string str2 = "forgeeksgeeks";
	int n = str1.size();
	str2 = str2 + str2;
	KMP(2 * n, n, str2, str1);
	return 0;
}