ErrLookup › donnemartin/interactive-coding-challenges

donnemartin/interactive-coding-challenges

120+ interactive Python coding interview challenges (algorithms and data structures). Includes Anki flashcards. · Python · 261 source files

Analyzed at 358f2cc604 on 2026-08-28. 107 documented errors.

Code / Message	Type	Severity	Tags
data cannot be None	validation	error	binary-search-tree, none-check, typeerror, validation
neighbor or weight cannot be None	validation	error	graph, adjacency-list, none-check, typeerror
neighbor cannot be None	validation	error	graph, adjacency-list, none-check, typeerror
neighbor not found	validation	error	graph, adjacency-list, keyerror, missing-edge
key cannot be None	validation	error	graph, node-key, none-check, typeerror
Invalid key	validation	error	graph, edge, keyerror, validation
key cannot be None	validation	error	min-heap, priority-queue, none-check, typeerror
word cannot be None	validation	error	trie, search, none-check, typeerror
word does not exist	validation	error	trie, remove, keyerror, word-not-found
num cannot be None	validation	error	fizz-buzz, input-validation, typeerror, none-check
num cannot be less than one	validation	error	fizz-buzz, range-validation, valueerror
Key not found	validation	error	hash-map, keyerror, key-not-found
str1 or str2 cannot be None	validation	error	string-diff, none-check, typeerror, validation
nums or target cannot be None	validation	error	two-sum, none-check, typeerror, validation
nums cannot be empty	validation	error	two-sum, empty-list, valueerror, validation
Invalid index	validation	error	python, bit-manipulation, index-error, argument-validation
number cannot be None	validation	error	python, constructor, type-error, none-check
Invalid value	validation	error	python, bit-manipulation, value-validation, generic-exception
a or b cannot be None	validation	error	python, hamming-distance, type-error, none-check
Invalid argument: None	validation	error	python, bit-manipulation, graphics, type-error, none-check
Invalid arg: Empty screen or width	validation	error	python, value-error, empty-buffer, graphics, argument-validation
Invalid arg: x1 or x2 out of bounds	validation	error	python, out-of-bounds, value-error, graphics, off-by-one
num cannot be None	validation	error	python, bit-manipulation, type-error, none-check
num cannot be None	validation	error	python, bit-manipulation, type-error, none-check
num cannot be 0 or negative	validation	error	python, value-error, bit-manipulation, non-positive-input
Argument cannot be None	validation	error	python, bit-manipulation, type-error, none-check
Index cannot be negative	validation	error	python, value-error, negative-index, bit-manipulation
num cannot be None	validation	error	python, bit-manipulation, type-error, none-check
data cannot be None	validation	error	python, bst, tree, type-error, none-check
root cannot be None	validation	error	python, bst, tree, empty-state, type-error
root must have at least one child	validation	error	python, bst, tree, insufficient-data, value-error
node cannot be None	exception	error	python, bst, successor, tree-traversal, none-check
root cannot be None	exception	error	python, binary-tree, none-check, validation
neighbor or weight cannot be None	exception	error	python, graph, none-check, edge-weight
neighbor cannot be None	exception	error	python, graph, none-check, edge-removal
neighbor not found	exception	error	python, graph, keyerror, edge-removal
key cannot be None	exception	error	python, graph, none-check, node-key
Invalid key	exception	error	python, graph, keyerror, edge-validation
graph cannot be None	exception	error	python, graph, dijkstra, none-check, constructor
Input node keys cannot be None	exception	error	python, graph, dijkstra, none-check
Invalid start or end node key	exception	error	python, graph, dijkstra, keyerror, validation
root cannot be None	exception	error	binary-tree, bst, none-guard, python
key cannot be None	exception	error	heap, none-guard, python
root is None	exception	error	tree, bfs, traversal, none-guard, python
root cannot be None	exception	error	tree, lca, ancestors, none-guard, python
word cannot be None	exception	error	trie, string, none-guard, python
word does not exist	exception	error	trie, keyerror, deletion, python
num cannot be None	exception	error	math, digits, none-guard, python
num cannot be negative	exception	error	math, digits, validation, python
num cannot be None	exception	error	python, input-validation, none-check, primes
max_num cannot be None	exception	error	python, input-validation, none-check, primes, sieve
val cannot be None	exception	error	python, input-validation, none-check, statistics
n cannot be None	exception	error	python, input-validation, none-check, bit-manipulation
a or b cannot be None	exception	error	python, input-validation, none-check, bit-manipulation, recursion
a or b cannot be None	exception	error	python, input-validation, none-check, bit-manipulation, recursion
greed_indices or cookie_sizes cannot be None	exception	error	python, input-validation, none-check, greedy, arrays
data cannot be None	exception	error	python, input-validation, none-check, intervals, sorting
Invalid event type	exception	error	python, enum, input-validation, intervals, event-processing
grid cannot be None	exception	error	python, input-validation, none-check, matrix, grid
license_key must be a str	exception	error	python, input-validation, none-check, strings, formatting
license_key must not be empty	exception	error	python, input-validation, empty-string, strings
file_system cannot be None	exception	error	python, input-validation, none-check, strings, file-paths
string cannot be None	exception	error	python, input-validation, none-check, strings, sliding-window
k cannot be None	exception	error	python, input-validation, none-check, sliding-window
val cannot be None	exception	error	python, input-validation, none-check, statistics
prices cannot be None	exception	error	python, input-validation, none-check, arrays, greedy
prices must have at least two values	validation	error	python, input-validation, algorithm, valueerror
array cannot be None	exception	error	python, null-check, input-validation, typeerror
nums cannot be None	exception	error	python, null-check, in-place, typeerror
array cannot be None	exception	error	python, null-check, brute-force, typeerror
array cannot be None	exception	error	python, null-check, in-place-sort, typeerror
array must have 3 or more ints	validation	error	python, input-validation, algorithm, valueerror
ransom_note or magazine cannot be None	exception	error	python, null-check, string, typeerror
sentence cannot be None	exception	error	python, input-validation, typeerror, algorithm
rows and cols cannot be None	exception	error	python, input-validation, typeerror, algorithm
rows and cols cannot be negative	validation	error	python, input-validation, valueerror, algorithm
s or t cannot be None	exception	error	python, input-validation, typeerror, strings
a or b cannot be None	exception	error	python, input-validation, typeerror, bit-manipulation, recursion
a or b cannot be None	exception	error	python, input-validation, typeerror, bit-manipulation, recursion
coins or total cannot be None	exception	error	python, input-validation, typeerror, dynamic-programming
Cannot have a None input	exception	error	python, input-validation, typeerror, recursion, hanoi
input_items or total_weight cannot be None	exception	error	python, dynamic-programming, knapsack, input-validation, typeerror
items or total_weight cannot be None	exception	error	python, knapsack, unbounded, dynamic-programming, input-validation
str input cannot be None	exception	error	python, dynamic-programming, string, lcs, input-validation
seq cannot be None	exception	error	python, dynamic-programming, subsequence, input-validation
string must be of type str	validation	error	python, type-check, string, sliding-window, input-validation
k must be of type int	validation	error	python, type-check, integer, sliding-window, input-validation
str input cannot be None	exception	error	python, dynamic-programming, string, substring, input-validation
matrices cannot be None	exception	error	python, dynamic-programming, matrix-chain, input-validation
prices or k cannot be None	exception	error	python, dynamic-programming, stocks, input-validation
num_pairs cannot be None	exception	error	python, recursion, backtracking, parentheses, input-validation
num_pairs cannot be < 0	validation	error	python, valueerror, recursion, backtracking, input-validation
num_steps cannot be None or negative	exception	error	python, recursion, memoization, dynamic-programming, input-validation
items cannot be None	exception	error	python, anagram, hashing, input-validation
data cannot be None	exception	error	python, sorting, insertion-sort, input-validation
source or dest cannot be None	exception	error	python, merge, array, input-validation, typeerror
end indices must be >= 0	exception	error	python, merge, array, valueerror, index-validation
data cannot be None	exception	error	python, input-validation, typeerror, merge-sort
array cannot be None or empty	exception	error	python, input-validation, typeerror, bit-manipulation
data cannot be None	exception	error	python, input-validation, typeerror, quick-sort
array cannot be None	exception	error	python, input-validation, typeerror, radix-sort
array or val cannot be None	exception	error	python, input-validation, typeerror, binary-search
matrix and val cannot be None	exception	error	python, input-validation, typeerror, matrix-search
data cannot be None	exception	error	python, input-validation, typeerror, selection-sort
Stack is full	exception	error	python, stack, overflow, capacity, data-structure
Stack is empty	exception	error	python, stack, underflow, data-structure
Stack full	exception	error	python, stack, capacity, overflow, data-structure