Counting Sort is a non-comparison sorting algorithm that works by counting how many times each value appears in an input array. Instead of comparing elements like typical sorting algorithms, it builds a frequency array and reconstructs the sorted result based on those counts. This approach makes Counting Sort extremely efficient when the range of values is limited.

For coding interviews, Counting Sort is important because it introduces the idea of frequency counting and prefix-based reconstruction. Many interview problems rely on this pattern when dealing with integer ranges, character frequencies, or bucket-style grouping. Understanding Counting Sort also helps you recognize when you can replace slower comparison-based approaches with linear-time solutions.

In practice problems, Counting Sort often appears in variations such as:

• Sorting integers when the value range is known
• Counting occurrences of elements efficiently
• Building cumulative counts using Prefix Sum techniques
• Serving as a subroutine in algorithms like Radix Sort

To master this topic, you should already be comfortable with Array manipulation and general Sorting concepts. The practice questions in this section will help you understand when Counting Sort is the right tool and how to implement it efficiently in coding interviews.