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13. Find Starting Node of Cycle ⭐

After collision, place p1 at head and keep p2 at collision. Both move 1 step; their meeting point is the exact cycle entrance.

Time O(n) Space O(1)

Open in 3D Studio

Live loop — open the studio to scrub, add your own array, or race it in Battle Arena.

Asked in interviews at

NetflixAmazonByteDance

Reference implementation (Python)

def detect_cycle_start(head):
    slow = fast = head
    while fast and fast.next:
        slow, fast = slow.next, fast.next.next
        if slow == fast: break
    else: return None
    p1, p2 = head, slow
    while p1 != p2:
        p1, p2 = p1.next, p2.next
    return p1

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<iframe src="/embed/cycle-start-node" width="100%" height="380" style="border:1px solid #e6e8ec;border-radius:14px" loading="lazy" title="3D algorithm visualization by CodeWithMunnaX"></iframe>

Frequently asked

What is the time and space complexity of 13. Find Starting Node of Cycle ⭐?

13. Find Starting Node of Cycle ⭐ runs in O(n) time and O(1) auxiliary space.

Is the 13. Find Starting Node of Cycle ⭐ visualizer free?

The core 3D visualizer, Web Audio chimes and step intuition are free. A one-time ₹49 Pro Pass unlocks advanced algorithms, large custom arrays, Battle Arena and reel export.

Which companies ask 13. Find Starting Node of Cycle ⭐ in interviews?

13. Find Starting Node of Cycle ⭐ shows up in interviews at Netflix, Amazon, ByteDance.

How does the 3D visualization of 13. Find Starting Node of Cycle ⭐ work?

Each array value becomes a 3D pillar whose height maps to its value. Comparisons glow amber, swaps flash red, and settled elements lock green while a floating pointer badge tracks the active index — synchronized line-by-line with the Python code.