Beta 0.42.0Beta

Dashboard
Learn
Exercises
Challenges
Visualizer

What's newv0.42.0

SearchSearch for a chapter, module, exercise, challenge, page, or profile

first_repeat

Your mission

Implement first_repeat, which returns the first value met a second time when values is read from left to right.

See it in action

first_repeat([6, 2, 9, 2, 6]): 2
first_repeat([5, -1, 0]): None
first_repeat([]): None

Your checklist

values is a list of int, possibly empty. Its items can be any int, negative and 0 included.
Read values from left to right and stop at the first position whose value already appeared at an earlier position. Return that value.
Return None when no value appears more than once.
Do not modify values.

Constraints

Expected file: first_repeat.py
Allowed functions: None. Write every helper yourself.

Run the tests to grade your code

20 tests

A value repeats later in the list
The earliest second occurrence wins, not the first value with a twin
Inner pair closes before the outer one
The first item comes back, not as a neighbour
Two equal neighbours at the end
0 is the repeated value
0 repeats before another value does
A negative value repeats
Large values, opposite signs differ
A value seen three times
All items equal
The value is returned, not its position
A list of two equal items
The repeat closes far from its first occurrence
No value repeats
A single 0
Empty list
Longer list with a late repeat
Longer list with no repeat
values is left unchanged

Python

Dashboard
Learn
Exercises
Challenges
Visualizer

first_repeat

Your mission

Implement first_repeat, which returns the first value met a second time when values is read from left to right.

See it in action

first_repeat([6, 2, 9, 2, 6]): 2
first_repeat([5, -1, 0]): None
first_repeat([]): None

Your checklist

values is a list of int, possibly empty. Its items can be any int, negative and 0 included.
Read values from left to right and stop at the first position whose value already appeared at an earlier position. Return that value.
Return None when no value appears more than once.
Do not modify values.

Constraints

Expected file: first_repeat.py
Allowed functions: None. Write every helper yourself.

Run the tests to grade your code

20 tests

A value repeats later in the list
The earliest second occurrence wins, not the first value with a twin
Inner pair closes before the outer one
The first item comes back, not as a neighbour
Two equal neighbours at the end
0 is the repeated value
0 repeats before another value does
A negative value repeats
Large values, opposite signs differ
A value seen three times
All items equal
The value is returned, not its position
A list of two equal items
The repeat closes far from its first occurrence
No value repeats
A single 0
Empty list
Longer list with a late repeat
Longer list with no repeat
values is left unchanged

Variables will appear here

Python