find the substring count from | CareerCup

find the substring count from | CareerCup
find the substring count from a string without string functions in java?
Given String str = "abcdefghcde";
String find = "cde";
Count occurrences of cde in String str

If space is no issue, you can use suffix tree. Time complexity: O(query length) 
Or you can use KMP algorithm it requires lesser space than suffix tree.
https://github.com/Simiopolis/careercup-java/blob/master/src/salesforce/SFCountSubstringsQ.java
    public static int substringsCount(String string, String pattern) {
        if(string == null || pattern == null)
            return -1;
        char[] str = string.toCharArray();
        char[] pat = pattern.toCharArray();
     
        int startIndex = 0;
        int lastIndex = 0;
        int count = 0;
     
        while(lastIndex < str.length) {
            if(lastIndex - startIndex >= pat.length || str[lastIndex] != pat[lastIndex-startIndex]) {
                startIndex++;
                lastIndex = startIndex;
            } else if(lastIndex - startIndex == pat.length-1) {
                count++;
                startIndex = lastIndex+1;
            }
            lastIndex++;
        }
        return count;
    }
https://github.com/Simiopolis/careercup-java/blob/master/src/salesforce/SFFindFirstOccurenceQ.java
 * Find the first index of the substring without using a java library
 * function or regular expressions.
    public static void main(String[] args) {
        System.out.println(firstIndexOfSubstring("dworldhellow world", "world"));
        // Test from Glassdoor.
        System.out.println(firstIndexOfSubstring("internnet", "net"));
    }

    public static int firstIndexOfSubstring(String s, String p) {
        int firstIndex = 0;
        int lastIndex = 0;
       
        while(lastIndex < s.length()) {
            // If there is an initial match, update firstIndex.
            if(s.charAt(lastIndex) == p.charAt(0))
                firstIndex = lastIndex;

            // If we have searched beyond the length of the pattern
            // or the pattern stopped matching, reset firstIndex.
            else if(lastIndex-firstIndex >= p.length() || s.charAt(lastIndex) != p.charAt(lastIndex-firstIndex))
                firstIndex = -1;

            // If everything checks and the last character of the pattern
            // is the same as the current string index, we've found
            // the first occurence.
            else if(s.charAt(lastIndex) == p.charAt(p.length()-1))
                return firstIndex;

            lastIndex++;
        }
        return firstIndex;
    }
Read full article from find the substring count from | CareerCup