Python List Problems

Python List Practice Problems

Median of a list

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Python Practice › List Programs › Program 100

Median of a list

EasyList Programs · 100 of 100

Write a Python program to get the median of all the elements of a list.

Input
[2, 4, 6, 7, 5, 8, 3, 11]
Output
[2, 3, 4, 5, 6, 7, 8, 11] 5.5 5.5

Approach

  1. Sort; for an even count average the two middle values.

Solution

Python
import statistics items = [2, 4, 6, 7, 5, 8, 3, 11]s = sorted(items)mid = len(s) // 2median = s[mid] if len(s) % 2 else (s[mid - 1] + s[mid]) / 2print(s, median, statistics.median(items))
Output
[2, 3, 4, 5, 6, 7, 8, 11] 5.5 5.5

Line by line

Line 5

Eight values, so the median is the average of the 4th and 5th sorted values, 5 and 6.

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Round every number and sum

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Python Practice › List Programs › Program 99

Round every number and sum

EasyList Programs · 99 of 100

Write a Python program to round every number in a list and print the sum of the rounded numbers multiplied by the list length.

Input
[22.4, 4.0, -16.22, -9.1, 11.0, -12.22, 14.2, -5.2, 17.5]
Output
[22, 4, -16, -9, 11, -12, 14, -5, 18]
243

Approach

  1. Round each value with round(), add them, multiply by the length.

Solution

Python
numbers = [22.4, 4.0, -16.22, -9.1, 11.0, -12.22, 14.2, -5.2, 17.5]rounded = [round(n) for n in numbers]print(rounded)print(sum(rounded) * len(numbers))
Output
[22, 4, -16, -9, 11, -12, 14, -5, 18]
243

Line by line

Line 2

round(17.5) is 18 and round(-12.22) is -12; ties go to the even number.

Note

The sum of the rounded numbers is 27; multiplied by the 9 items it is 243.

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#100EasyMedian of a list

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Decode a run-length encoded list

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Python Practice › List Programs › Program 98

Decode a run-length encoded list

MediumList Programs · 98 of 100

Write a Python program to decode a run-length encoded list, where [n, x] means x repeated n times.

Input
[[2, 1], 2, 3, [2, 4], 5, 1]
Output
[1, 1, 2, 3, 4, 4, 5, 1]

Approach

  1. Expand [n, x] pairs; copy plain items.

Solution

Python
encoded = [[2, 1], 2, 3, [2, 4], 5, 1]decoded = []for item in encoded:    if isinstance(item, list):        count, value = item        decoded.extend([value] * count)    else:        decoded.append(item)print(decoded)
Output
[1, 1, 2, 3, 4, 4, 5, 1]

Line by line

Lines 5-6

[value] * count repeats the value.

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Remove repeated dictionaries

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Python Practice › List Programs › Program 97

Remove repeated dictionaries

EasyList Programs · 97 of 100

Write a Python program to remove repeated dictionaries from a list.

Input
[{"Hello": 5}, {"student": 7}, {"are": 3}, {"learning": 8}, {"Hello": 5}, {"Language": 8}, {"are": 3}]
Output
[{'Hello': 5}, {'student': 7}, {'are': 3}, {'learning': 8}, {'Language': 8}]

Approach

  1. Use a set of each dict’s items (as a frozenset) to remember what was seen.

Solution

Python
data = [{"Hello": 5}, {"student": 7}, {"are": 3}, {"learning": 8}, {"Hello": 5}, {"Language": 8}, {"are": 3}]seen = set()result = []for d in data:    key = frozenset(d.items())    if key not in seen:        seen.add(key)        result.append(d)print(result)
Output
[{'Hello': 5}, {'student': 7}, {'are': 3}, {'learning': 8}, {'Language': 8}]

Line by line

Line 4

frozenset(d.items()) is a hashable fingerprint of the dict, so the check is fast even for long lists.

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Word lengths as a dictionary

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Python Practice › List Programs › Program 96

Word lengths as a dictionary

EasyList Programs · 96 of 100

Write a Python program to build a dictionary of each word and its length.

Input
["Hello", "student", "are", "learning", "Python", "Its", "Language"]
Output
{'Hello': 5, 'student': 7, 'are': 3, 'learning': 8, 'Python': 6, 'Its': 3, 'Language': 8}

Approach

  1. A dict comprehension.

Solution

Python
words = ["Hello", "student", "are", "learning", "Python", "Its", "Language"]print({w: len(w) for w in words})
Output
{'Hello': 5, 'student': 7, 'are': 3, 'learning': 8, 'Python': 6, 'Its': 3, 'Language': 8}

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#97EasyRemove repeated dictionaries#98MediumDecode a run-length encoded list#99EasyRound every number and sum#100EasyMedian of a list

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Remove the 2nd character of each word

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Python Practice › List Programs › Program 95

Remove the 2nd character of each word

EasyList Programs · 95 of 100

Write a Python program to remove the 2nd character of each word.

Input
["Hello", "student", "are", "learning", "Python", "Its", "Python", "Language"]
Output
['Hllo', 'sudent', 'ae', 'larning', 'Pthon', 'Is', 'Pthon', 'Lnguage']

Approach

  1. Join the slices before and after index 1.

Solution

Python
words = ["Hello", "student", "are", "learning", "Python", "Its", "Python", "Language"]print([w[0] + w[2:] for w in words])
Output
['Hllo', 'sudent', 'ae', 'larning', 'Pthon', 'Is', 'Pthon', 'Lnguage']

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#96EasyWord lengths as a dictionary#97EasyRemove repeated dictionaries#98MediumDecode a run-length encoded list#99EasyRound every number and sum

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Capitalise the 3rd character of each word

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Python Practice › List Programs › Program 94

Capitalise the 3rd character of each word

EasyList Programs · 94 of 100

Write a Python program to make the 3rd character of each word uppercase.

Input
["Hello", "student", "are", "learning", "Python", "Its", "Python", "Language"]
Output
['HeLlo', 'stUdent', 'arE', 'leArning', 'PyThon', 'ItS', 'PyThon', 'LaNguage']

Approach

  1. Index 2 is the 3rd character; rebuild the word around it.

Solution

Python
words = ["Hello", "student", "are", "learning", "Python", "Its", "Python", "Language"]print([w[:2] + w[2].upper() + w[3:] if len(w) > 2 else w for w in words])
Output
['HeLlo', 'stUdent', 'arE', 'leArning', 'PyThon', 'ItS', 'PyThon', 'LaNguage']
Note

The original sample changed the 4th character (“HelLo”). The 3rd character is index 2, which gives “HeLlo”.

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#95EasyRemove the 2nd character of each word#96EasyWord lengths as a dictionary#97EasyRemove repeated dictionaries#98MediumDecode a run-length encoded list

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Replace a word in a list

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Python Practice › List Programs › Program 93

Replace a word in a list

EasyList Programs · 93 of 100

Write a Python program to replace “Java” with “Python” in a list of words.

Input
["Hello", "student", "are", "learning", "Java", "Its", "Java", "Language"]
Output
['Hello', 'student', 'are', 'learning', 'Python', 'Its', 'Python', 'Language']

Approach

  1. Map each word, replacing the match.

Solution

Python
words = ["Hello", "student", "are", "learning", "Java", "Its", "Java", "Language"]print(["Python" if w == "Java" else w for w in words])
Output
['Hello', 'student', 'are', 'learning', 'Python', 'Its', 'Python', 'Language']

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Dictionary from sublists

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Python Practice › List Programs › Program 92

Dictionary from sublists

EasyList Programs · 92 of 100

Write a Python program to create a dictionary from [key, value] sublists.

Input
[["a", 5], ["b", 8], ["c", 11], ["d", 14], ["e", 23]]
Output
{'a': 5, 'b': 8, 'c': 11, 'd': 14, 'e': 23}

Approach

  1. dict() accepts pairs directly.

Solution

Python
print(dict([["a", 5], ["b", 8], ["c", 11], ["d", 14], ["e", 23]]))
Output
{'a': 5, 'b': 8, 'c': 11, 'd': 14, 'e': 23}

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Tuples to sublists

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Python Practice › List Programs › Program 91

Tuples to sublists

EasyList Programs · 91 of 100

Write a Python program to convert the tuples in a list into lists.

Input
[(3, 5), (6, 8), (8, 11), (12, 14), (17, 23)]
Output
[[3, 5], [6, 8], [8, 11], [12, 14], [17, 23]]

Approach

  1. list(t) for each tuple.

Solution

Python
data = [(3, 5), (6, 8), (8, 11), (12, 14), (17, 23)]print([list(t) for t in data])
Output
[[3, 5], [6, 8], [8, 11], [12, 14], [17, 23]]

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#92EasyDictionary from sublists#93EasyReplace a word in a list#94EasyCapitalise the 3rd character of each word#95EasyRemove the 2nd character of each word

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