Anagram Substring Search (Or Search for all permutations)

Given a text txt[0..n-1] and a pattern pat[0..m-1], write a function search(char pat[], char txt[]) that prints all occurrences of pat[] and its permutations (or anagrams) in txt[]. You may assume that n > m. 
Expected time complexity is O(n)

Examples:

1) Input:  txt[] = "BACDGABCDA"  pat[] = "ABCD"
   Output:   Found at Index 0
             Found at Index 5
             Found at Index 6
2) Input: txt[] =  "AAABABAA" pat[] = "AABA"
   Output:   Found at Index 0
             Found at Index 1
             Found at Index 4

// C++ program to search all anagrams of a pattern in a text #include<iostream> #include<cstring> #define MAX 256 using namespace std; // This function returns true if contents of arr1[] and arr2[] // are same, otherwise false. bool compare(char arr1[], char arr2[]) {     for (int i=0; i<MAX; i++)         if (arr1[i] != arr2[i])             return false;     return true; } // This function search for all permutations of pat[] in txt[] void search(char *pat, char *txt) {     int M = strlen(pat), N = strlen(txt);     // countP[]:  Store count of all characters of pattern     // countTW[]: Store count of current window of text     char countP[MAX] = {0}, countTW[MAX] = {0};     for (int i = 0; i < M; i++)     {         (countP[pat[i]])++;         (countTW[txt[i]])++;     }     // Traverse through remaining characters of pattern     for (int i = M; i < N; i++)     {         // Compare counts of current window of text with         // counts of pattern[]         if (compare(countP, countTW))             cout << "Found at Index " << (i - M) << endl;         // Add current character to current window         (countTW[txt[i]])++;         // Remove the first character of previous window         countTW[txt[i-M]]--;     }     // Check for the last window in text     if (compare(countP, countTW))         cout << "Found at Index " << (N - M) << endl; } /* Driver program to test above function */ int main() {     char txt[] = "BACDGABCDA";     char pat[] = "ABCD";     search(pat, txt);     return 0; }

Output:

Found at Index 0
Found at Index 5
Found at Index 6