First and last occurrence for binary search in C

Question

I\'m trying to understand how do I modify the binary search for it work for first and last occurrences, surely I can find some code on the web but I\'m trying to reach deep

Answer 1

Just perform a normal binary search for the element (e). Let's say it returns index i. To find the index of the first occurrence just do a binary search for e on [0<->i-1] repeatedly until the search can't find e anymore. Similarly do [i+1<->n] for last occurrence.