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Interactive Python Lab

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PyAnimate

Interactive Python Lab

AI Wisdom

Interactive Python Lab

Fibonacci (Iterative)

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Data Flow Pipeline

beginner Track

Loop Explorer

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Factorial (Iterative)

Fibonacci (Iterative)

Count Occurrences

Reverse a List

Palindrome Check

Find Min & Max

Sum & Average

FizzBuzz

Explain

Line 1

Compute first 7 Fibonacci numbers.

Why this approach?

The Fibonacci sequence: 0, 1, 1, 2, 3, 5, 8, 13, 21... Each number is the sum of the previous two. We choose n=7 to show enough of the sequence to see the pattern clearly.

Structured Explanation

Overview

Iterative Fibonacci builds up the sequence using two variables, no recursion needed.

Analogy

Leapfrog: always remember only the last two steps you took.

Step-by-step

Start with a=0, b=1.
Loop n-1 times: a, b = b, a+b.
After the loop, a holds fib(n).

Visual

a=0,b=1 → a=1,b=1 → a=1,b=2 → a=2,b=3 → a=3,b=5

Common mistakes

Off-by-one in loop count.
Using a list to store all values when only the last two are needed.

Practice questions

Print the first 20 Fibonacci numbers.
Find the first Fibonacci number > 1000.

Time

O(n)

Space

O(1)

Complexity

Time

O(n)

Space

O(1)

Complexity Overview

O(1)space

O(log n)

O(n)time

O(n log n)

O(n²)

n = 8range 1-20

AT N = 8

Complexity	Operations
O(1)	1
O(log n)	3
O(n)	8
O(n log n)	24
O(n²)	64

Challenge

Generate the first 15 Fibonacci numbers using only two rolling variables (no list).

Hint

Keep track of prev and curr. Each step: new_curr = prev + curr, then shift: prev = curr, curr = new_curr.

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