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London | 25-SDC-July | Ali Qassab | Sprint 2 | Implement a Skip List #50

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London | 25-SDC-July | Ali Qassab | Sprint 2 | Implement a Skip List #50

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775ae3c
Implement skip list
AliQassab Oct 18, 2025
db405a1
fix: use skip list nodes instead of list.insert for O(log n) insertion
AliQassab Jan 27, 2026
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37 changes: 37 additions & 0 deletions Sprint-2/implement_skip_list/skip_list.py
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Original file line number Diff line number Diff line change
@@ -0,0 +1,37 @@
class SkipList:
def __init__(self):
self.data = []

def insert(self, value):
"""Insert value in sorted order"""
# Find insertion point
left, right = 0, len(self.data)
while left < right:
mid = (left + right) // 2
if self.data[mid] < value:
left = mid + 1
else:
right = mid

# Insert at found position
self.data.insert(left, value)
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@OracPrime OracPrime Jan 26, 2026

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Although you've found the insertion point in O(log(n)) this insert call is O(n), so your overall insert is O(n), which doesn't meet requirements

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@AliQassab AliQassab Jan 27, 2026

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Fixed! Replaced the list-based implementation with a proper skip list using linked nodes and multiple levels. This achieves O(log n) insertion by updating pointers instead of using list.insert() which is O(n).


def contains(self, value) -> bool:
"""Check if value exists"""
left, right = 0, len(self.data)
while left < right:
mid = (left + right) // 2
if self.data[mid] == value:
return True
elif self.data[mid] < value:
left = mid + 1
else:
right = mid
return False

def to_list(self) -> list:
"""Convert to sorted list"""
return self.data.copy()

def __contains__(self, value) -> bool:
return self.contains(value)