Mission Dashboard
Vidya Python Core
Level 4 — Data Structures — Stacks, queues, linked lists, trees, graphs, hash maps, and heaps.
Active Mission PayloadLIFO / FIFO Sutra
Stacks & Queues
Implement stack and queue ADTs using Python lists and collections.deque.
Python Sandbox Preview
from collections import deque
queue = deque()
queue.append("A")
queue.append("B")
print(queue.popleft()) # AUTF-8 · Interactive Sandbox Target Code
What this Mission Builds
Stacks (LIFO) and queues (FIFO) are the foundation of undo systems, BFS, expression parsing, and more.
•Build a stack with push/pop/peek
•Build a queue with deque for O(1) operations
•Apply stacks to balance-checking and expression evaluation
Duration
55 min
Difficulty
3/5
Rank Reward
+150 XP
Practice Lab — 📚 Stacks & Queues
15 Coding Challenges · 5 Difficulty Tiers
Complete all tiers to earn up to 1,720 XP and unlock the next chapter.
🟢Beginner Tier3 programs · +165 XP
📚#1
+50 XPStack Push & Pop
Simulate a stack with a Python list and process push/pop commands
stacklist.append 6m
🚶#2
+55 XPQueue with Deque
Simulate a FIFO queue using collections.deque
queuecollections.deque 7m
🔄#3
+60 XPReverse a String with a Stack
Use a stack to reverse words in a sentence
stacklist.append 7m
🔵Intermediate Tier3 programs · +265 XP
🔗#1
+80 XPBalanced Parentheses Checker
Use a stack to verify that brackets are properly matched and nested
stackbracket matching 10m
🧮#2
+90 XPPostfix Expression Evaluator
Evaluate a Reverse Polish Notation expression using a stack
stackpostfix evaluation 12m
📈#3
+95 XPNext Greater Element
Find the next greater element for each item using a stack
stacknext greater element 13m
🟡Advanced Tier3 programs · +345 XP
📊#1
+110 XPMonotonic Stack: Stock Span
Compute the stock span for each day using a monotonic stack
monotonic stackstock span 14m
🪟#2
+115 XPSliding Window Maximum with Deque
Find the maximum in every window of size k in O(n) using a monotonic deque
collections.dequemonotonic deque 15m
🔁#3
+120 XPQueue Using Two Stacks
Implement a FIFO queue using only two Python lists as stacks
two-stack queueamortized O(1) 15m
🔴LeetCode Tier3 programs · +430 XP
✅#1
+130 XPValid Parentheses (Multiple Types)
Determine if a bracket string is valid — classic LeetCode #20
stackvalid parentheses 16m
🌡️#2
+145 XPDaily Temperatures
For each day, find how many days until a warmer temperature — LeetCode #739
monotonic stackdaily temperatures 18m
📉#3
+155 XPMin Stack
Design a stack that supports push, pop, top, and getMin in O(1) — LeetCode #155
MinStackauxiliary stack 20m
🏆Hackathon Tier3 programs · +515 XP
🌐#1
+160 XPBrowser History Simulator
Simulate browser back/forward navigation using two stacks
two stacksbrowser history 28m
📋#2
+170 XPTask Scheduler with Undo
Process tasks with a queue and support multi-level undo using a stack
dequestack for undo 30m
🔢#3
+185 XPInfix to Postfix Converter
Convert an infix expression to postfix using the shunting-yard algorithm
shunting-yard algorithminfix to postfix 35m
Complete all 5 tiers to earn the Stacks & Queues Master badge
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