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25 problems asked at Meta.

Easy (5)

Implement Queue using Stacks (LeetCode 232)

Stack, Queue

Leetcode 1710 — Maximum Units on a Truck

Greedy, Sorting

Stack using Queue (LeetCode 225)

Stack, Queue

Two Sum (Leetcode 1)

Two Pointers, Arrays

Valid Parentheses (Leetcode 20)

Stack, Strings

Medium (9)

Find All Duplicates in an Array (LC 442)

Arrays

Find duplicate number (LC-287)

Arrays, Two Pointers, Linked Lists

Gas Station (Leetcode 134)

Arrays, Greedy, Prefix Sum

Implementation of Deque using Circular Array (Leetcode 641)

Queue, Arrays

Magnetic Force Between Two Balls / Aggressive Cows

Searching, Greedy

Min Stack (Leetcode 155)

Stack

Remove Duplicate Letters / Smallest Subsequence of Distinct Characters (Leetcode 316 / 1081)

Strings, Greedy, Hashing...

Repeated Substring Pattern (Leetcode 459)

Strings

Stock Span Problem (Leetcode 901)

Stack, Arrays, Greedy

Hard (11)

Capacity to Ship Packages Within D Days

Searching, Greedy

First Missing Positive (LC 41)

Arrays, Sorting, Hashing

Largest Rectangle in Histogram (leetcode 84)

Arrays, Stack

Maximal Rectangle (Leetcode 85) (largest rectangle with all 1's)

Matrix, Stack

N-Queens (Leetcode 51 & 52)

Backtracking, Maths, Recursion...

Next Permutation (Leetcode 31)

Arrays, Greedy, Two Pointers

Postfix to Infix & Evaluation of Postfix (Leetcode 150)

Stack

Repeating Element (Cycle + Expected Sum appr.)

Arrays, Two Pointers, Linked Lists

Shortest Palindrome (Leetcode 214)

Strings, Greedy

Split Array Largest Sum

Searching, Greedy

Trapping Rain Water (LC 42)

Two Pointers, Prefix and Suffix Arrays, Stack