Python Coding challenge - Day 543| What is the output of the following Python Code?

 

Code Explanation:

Function Purpose

def has_cycle(nums):

This function checks whether there is a cycle in a list of numbers.

It uses the Floyd’s Cycle Detection Algorithm (also known as Tortoise and Hare) to detect cycles without extra space.

Initialize Pointers

    slow = fast = 0

Two pointers, slow and fast, are both initialized at index 0.

slow will move one step at a time, while fast moves two steps.

The idea is: if there is a cycle, slow and fast will eventually meet inside the cycle.

Loop to Traverse the List

    while fast < len(nums) and nums[fast] < len(nums):

The loop continues as long as:

fast is a valid index (< len(nums))

nums[fast] is also a valid index (we’re using it as a pointer too)

This prevents index out of range errors when accessing nums[nums[fast]].

Move Pointers

        slow = nums[slow]

        fast = nums[nums[fast]]

slow = nums[slow] → move slow pointer one step forward.

fast = nums[nums[fast]] → move fast pointer two steps forward.

This simulates two pointers moving at different speeds through the list.

Cycle Detection Condition

        if slow == fast:

            return True

If at any point slow and fast pointers meet, a cycle is detected.

In a cycle, fast-moving and slow-moving pointers will eventually catch up.

No Cycle Case

    return False

If the loop exits without the pointers meeting, there’s no cycle in the list.

Function Call and Output

print(has_cycle([1, 2, 3, 4, 2]))

The list is:

Index → Value

0 → 1, 1 → 2, 2 → 3, 3 → 4, 4 → 2

This forms a cycle: 2 → 3 → 4 → 2...

Pointers will move like this:

slow = 0 → 1 → 2 → 3

fast = 0 → 2 → 4 → 3 → 2

At some point, slow == fast == 2, so:

Output:

True

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