First and Last Occurrence of Element in DSA Go - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does 'First Occurrence of Element' mean in an array?

It means finding the index of the first time a given element appears in the array when reading from left to right.

beginner

What is the difference between 'First Occurrence' and 'Last Occurrence' of an element?

First Occurrence is the earliest index where the element appears; Last Occurrence is the latest index where the element appears in the array.

intermediate

Why is binary search useful for finding first and last occurrences in a sorted array?

Binary search helps find the target element quickly by dividing the search space in half repeatedly, making it efficient to find first and last positions without scanning the whole array.

beginner

In Go, what is a simple way to represent the result of first and last occurrence search?

Use two integers representing the first and last index positions. If the element is not found, return -1 for both.

intermediate

What is the time complexity of finding first and last occurrence using binary search?

The time complexity is O(log n) because binary search divides the search space in half each step.

What should be returned if the element is not found in the array?

A Nil or null

B 0 for both first and last occurrence

C Length of the array

D -1 for both first and last occurrence

Returning -1 indicates the element does not exist in the array.

Which search method is most efficient for finding first and last occurrence in a sorted array?

A Depth-first search

B Linear search

C Binary search

D Breadth-first search

Binary search efficiently finds elements in sorted arrays by halving the search space.

If an element appears multiple times, what does 'last occurrence' mean?

A The last index where element appears

B The first index where element appears

C The middle index of appearances

D The count of appearances

Last occurrence is the highest index where the element is found.

What is the initial search range for binary search in an array of length n?

A From 1 to n

B From 0 to n-1

C From -1 to n

D From 0 to n

Array indices start at 0, so the range is 0 to n-1.

Which of these is NOT a correct step in finding first occurrence using binary search?

A Stop immediately when element is found without checking neighbors

B Move right if element is greater than mid element

C Move left if element found to check earlier indices

D Update result when element is found

We continue searching left to find the earliest occurrence, not stop immediately.

Explain how to find the first and last occurrence of an element in a sorted array using binary search.

Think about narrowing down the search to find earliest and latest positions.

Describe the difference between linear search and binary search for finding occurrences of an element.

Compare how each method moves through the array.