Count and Say Problem in DSA Python - Build from Scratch

Count and Say Problem

📖 Scenario: Imagine you are working with a special sequence of numbers called the "Count and Say" sequence. Each number in the sequence describes the previous number by counting the digits in groups. For example, starting with "1", the next number says "one 1" which is "11", then "two 1s" which is "21", and so on.

🎯 Goal: You will build a program that generates the nth number in the Count and Say sequence. This helps understand how to process strings and count repeating characters step-by-step.

📋 What You'll Learn

Create a starting string for the sequence

Set a number n to decide which term to generate

Write a loop to build the sequence up to n

Print the final sequence string

💡 Why This Matters

🌍 Real World

The Count and Say sequence is a simple example of run-length encoding, a technique used in data compression.

💼 Career

Understanding string processing and loops is essential for many programming tasks, including parsing data and implementing algorithms.

1

Create the starting string for the Count and Say sequence

Create a variable called current_term and set it to the string "1" as the first term of the sequence.

DSA Python

# Create the starting string for the sequence
# Your code here

Hint

The first term of the Count and Say sequence is always the string "1".

2

Set the term number to generate

Create a variable called n and set it to 5 to generate the 5th term of the sequence.

DSA Python

current_term = "1"
# Set the term number 'n' to 5
# Your code here

Hint

Choose a number n to decide which term of the sequence you want to find.

3

Build the Count and Say sequence up to the nth term

Write a for loop that runs from 1 to n - 1. Inside the loop, create a new string next_term by counting consecutive digits in current_term. Update current_term to next_term at the end of each loop.

DSA Python

current_term = "1"
n = 5
# Build the sequence up to the nth term
# Your code here

Hint

Use a nested loop to count repeated digits and build the next term string.

4

Print the nth term of the Count and Say sequence

Write a print statement to display the value of current_term which is the nth term of the sequence.

DSA Python

current_term = "1"
n = 5
for _ in range(1, n):
    next_term = ""
    count = 1
    for i in range(1, len(current_term)):
        if current_term[i] == current_term[i - 1]:
            count += 1
        else:
            next_term += str(count) + current_term[i - 1]
            count = 1
    next_term += str(count) + current_term[-1]
    current_term = next_term
# Print the nth term
# Your code here

Hint

The 5th term of the Count and Say sequence is "111221".