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Algorithms & data structures

Classic patterns — search, sort, stacks, queues, and practical complexity-aware code.

5 matches

How to Get the Breadth-First Traversal Order of a Graph in Python

Performs a breadth-first search on an adjacency list and returns the order nodes are visited, using a deque for efficient queue operations.

graph bfs queue

Python

from collections import deque

def bfs_order(adjacency, start=0):
    """Return the order nodes are visited in a breadth-first traversal."""
    visited = set()
    order = []
    queue = deque([start])
    visited.add(start)

    while queue:
        node = queue.popleft()
        order.append(node)

        for neig…

14 0 Open

Algorithms & data structures easy

How to Heapify a List into a Min Heap with heapq in Python

Convert any list into a valid min heap in-place using Python's heapq.heapify(), then pop the smallest element to verify heap order.

heapq min heap heapify

Python

import heapq

data = [5, 3, 8, 1, 9, 2, 7, 4, 6]
print("Original list:", data)

heapq.heapify(data)
print("Min heap:", data)

popped = heapq.heappop(data)
print("Smallest element popped:", popped)
print("Heap after pop:", data)

14 0 Open

Algorithms & data structures easy

How to Implement a Moving Average from a Data Stream in Python

Implement a MovingAverage class using a deque and running sum to compute the average of the last k values from a continuous data stream.

deque sliding-window streaming

Python

from collections import deque

class MovingAverage:
    def __init__(self, size):
        self.size = size
        self.queue = deque()
        self.window_sum = 0

    def next(self, val):
        self.queue.append(val)
        self.window_sum += val

        if len(self.queue) > self.size:
            self.window_su…

12 0 Open

Algorithms & data structures easy

How to Implement a Recent Counter with a Deque in Python

Implements a RecentCounter class that uses a deque to count ping requests within the last 3000 milliseconds.

deque recents sliding-window

Python

from collections import deque
import time


class RecentCounter:
    def __init__(self):
        self.hits = deque()

    def ping(self, t: int) -> int:
        self.hits.append(t)
        while self.hits and self.hits[0] < t - 3000:
            self.hits.popleft()
        return len(self.hits)


if __name__ == "__mai…

11 0 Open

Algorithms & data structures easy

Implement Queue Using Two Stacks in Python

Python class that implements a FIFO queue using two stacks, with enqueue, dequeue, peek, and emptiness checks.

queue stack data-structures

Python

class QueueUsingStacks:
    def __init__(self):
        self.stack_in = []
        self.stack_out = []

    def enqueue(self, value):
        self.stack_in.append(value)

    def dequeue(self):
        if not self.stack_out:
            while self.stack_in:
                self.stack_out.append(self.stack_in.pop())
  …

13 0 Open

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