Given a string str consisting of lowercase English alphabets, the task is to find the count of substrings that start with “geeks” and end with “for”.
Input: str = “geeksforgeeksisforgeeks”
“geeksfor”, “geeksforgeeksisfor” and “geeksisfor”
are the only valid substrings.
Input: str = “geeksforgeeks”
Naive approach: First set the counter to 0 then iterate over the string and whenever the substring “geeks” is encountered, from the very next indices again iterate over the string and try to find the substring “for”. If “for” is present then increment the counter and finally print it.
Efficient approach: Set two counter for the substrings “geeks” and “for”, say c1 and c2. On iterating, whenever the substring “geeks” is encountered, increment c1 and whenever “for” is encountered, set c2 = c2 + c1. This is because every occurrence of “geeks” will make a valid substring with the current found “for”. Finally print c2.
Below is the implementation of the above approach:
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