Searching Algorithms

Searching algorithms are essential tools in computer science used to locate specific items within a collection of data. In this tutorial, we are mainly going to focus upon searching in an array. When we search an item in an array, there are two most common algorithms used based on the type of input array.

• Linear Search : It is used for an unsorted array. It mainly does one by one comparison of the item to be search with array elements. It takes linear or O(n) Time.
• Binary Search : It is used for a sorted array. It mainly compares the array's middle element first and if the middle element is same as input, then it returns. Otherwise it searches in either left half or right half based on comparison result (Whether the mid element is smaller or greater). This algorithm is faster than linear search and takes O(Log n) time.

Basics

• Introduction

Binary Search Implementations

• binary_search, lower_bound and upper_bound in C++
• Arrays.binarySearch() in Java
• Arrays.binarySearch() in Java for Search in subarray
• Collections.binarySearch() in Java
• Bisect in Python
• List.BinarySearch in C#

Easy Problems

• Largest in an Array
• Second Largest in an array
• Largest three in an array
• Missing Number
• First Repeating
• Missing and Repeating
• Count 1’s in a sorted binary array
• k largest(or smallest) Elements
• Kth smallest in row and column-wise sorted
• Common elements in 3 sorted
• Ceiling & Floor in a Sorted
• Max in a Bitonic
• More than n/k times Appearing

Medium Problems

• Triplets with zero sum
• Partition Point
• Largest pair sum
• K’th Smallest in Unsorted Array
• Search, Min & Max in a Sorted & Rotated
• Peak element
• Fixed Point
• K Most Frequent
• K Closest
• Binary Search for Rationals
• Missing in AP

Hard Problems

• Median of two sorted of same sizes
• Median of two sorted of different sizes
• Search in an almost sorted
• Search in a sorted infinite
• Pair sum in a sorted and rotated
• K’th Smallest/Largest in Unsorted
• K’th largest in a stream

More Searching Algorithms

• Sentinel Linear Search
• Meta Binary Search
• Ternary Search
• Jump Search
• Interpolation Search
• Exponential Search
• Fibonacci Search
• Best First Search (Informed Search)

Quick Links:

• Practice Problems on Searching
• Searching Interview Questions
• Quiz on Searching
• DSA Tutorial