Remove Nth Node From End of List

LeetCode 19 • Medium • Linked Lists

Remove the n-th node from the end. Dummy + two pointers: move fast n steps, then move both until fast.next is null.

TimeO(L)single pass

SpaceO(1)two pointers

Slow: — Fast: —

Slow

Fast

To remove

Slow

—

Fast

—

Result

pending

Speed:

Ready

Press Play. Dummy node + two pointers. Move fast n steps ahead, then move both until fast.next is null. slow.next = slow.next.next.

✎ Whiteboard

Size:3

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Practice until you don't need to look. Use the guide comments below as scaffolding. The green highlights are the nuances to burn into memory.

# ─── REMOVE NTH FROM END (LeetCode 19) ───

# Pattern: Dummy + two pointers — fast n steps ahead, then move both

# Time: O(n) Space: O(1)

# 1. Define: removeNthFromEnd(head, n)

# 2. Dummy: dummy = ListNode(0); dummy.next = head

# 3. Init: slow = fast = dummy

# 4. Advance fast n steps: for _ in range(n): fast = fast.next

# 5. Move both until fast at end: while fast.next: slow, fast = slow.next, fast.next

# 6. Remove: slow.next = slow.next.next

# 7. Return: return dummy.next

# Vars: dummy, slow, fast

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