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Arrays coding challenges
Practise arrays with 31 coding challenges, from easy to hard. Every challenge runs in your browser with instant tests, an AI review of your code and community solutions to compare.
Easy · 27 Medium · 3 Hard · 1
Skills you'll practise: ListsSingle passSortingTwo pointers2D arrays2D lists8-neighbor checksAccumulatorsAmortised costArithmetic seriesArray indexingAsync/await
- Python · C++ · C#
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- Community solutions
- 226
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- 3
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All challenges
Search by topic, language, or difficulty.
Easy
Count Pairs With a Sum
Count pairs of positions whose values add up to a target.
You'll learn
Pairs of indexesAvoiding double counts
No solutions yet
Hard
Trapping Rain Water
Compute how much rain water an elevation map holds.
You'll learn
Two pointersPrefix maxima
No solutions yet
Easy
Min and Max Together
Find the smallest and largest value in one pass.
You'll learn
Single passMultiple return values
No solutions yet
Medium
Minesweeper Neighbor Counts
Annotate a rectangular board.
You'll learn
8-neighbor checksBoundary handling
No solutions yet
Easy
Make an Array Nondecreasing
Find the fewest increments needed so each value is at least the previous one.
You'll learn
Greedy fixesRunning maximum
No solutions yet
Medium
Smallest Missing Coin Sum
Find the first positive amount that cannot be made from the available coins.
You'll learn
Reachable sumsSorting first
No solutions yet
Easy
Remove Duplicates
Keep only the first occurrence of each value.
You'll learn
Seen-value trackingOrder preservation
No solutions yet
Easy
Missing Number
Find the one number missing from 0..n.
You'll learn
Arithmetic seriesSum difference trick
No solutions yet
Medium
Nearest Smaller Value to the Left
For each number, find the closest earlier position containing a strictly smaller number.
You'll learn
Monotonic stackLinear time
No solutions yet
Easy
Cart Total With Discount
Total a shopping cart and apply a discount above a threshold.
You'll learn
ListsDiscount rules
No solutions yet
Easy
Swap First and Last
Exchange the first and last items of a list.
You'll learn
List indexingSwapping
No solutions yet
Easy
First Negative Index
Find where the first negative number appears.
You'll learn
Linear searchEarly return
No solutions yet
Easy
Median of a List
Find the middle value of a list after sorting.
You'll learn
SortingStatistics
No solutions yet
Easy
Count Positive Numbers
Count the values greater than zero in a list.
You'll learn
ListsCounting
No solutions yet
Easy
Above-Average Values
Keep the values that are greater than the average.
You'll learn
Two passesFiltering
No solutions yet
Easy
Array Minimum
Find the smallest value in a list.
You'll learn
Tracking a minimumSingle pass
No solutions yet
Easy
Array Maximum
Find the largest value in a list.
You'll learn
Tracking a maximumSingle pass
No solutions yet
Easy
Second Largest Value
Find the second largest distinct value.
You'll learn
Two trackersDistinct values
No solutions yet
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