Substring check

Given a string s and sub-string sub, find if it exists.

Algorithm

1. Compare every char of s with sub, if there is a match increment both pts and proceed
2. If there is no match then reset subPtr and proceed with sPtr.

Code

bool substringExists(string& str, string& substr) {
    int m = str.size();
    int n = substr.size();

    if(m == 0 || n == 0 || m < n)
        return FALSE;

    int j = 0;
    for(int i=0; i<m; i++) {
        int k = i;
        while(str[k].compare(substr[j]) == 0 && j < n) {
            k++; j++;
        }
        if(j == n+1) return TRUE;
        else j = 0;
    }

    return FALSE;
}

Time complexity

O(mn), where m is the length of string s, and n is the length of substring sub.