Python: Check if a given list is strictly increasing or not

Last update on December 21 2024 13:11:39 (UTC/GMT +8 hours)

Check Strictly Increasing List

Write a Python program to check if a given list increases strictly. Moreover, if removing only one element from the list results in a strictly increasing list, we still consider the list true.

Visual Presentation:

Sample Solution:

Python Code:

# Source: https://bit.ly/3qZqcwm
# Define a function called 'almost_increasing_sequence' that checks if a given sequence is an almost increasing sequence.
def almost_increasing_sequence(sequence):
    # Check if the length of the sequence is less than 3, and if so, return True.
    if len(sequence) < 3:
        return True

    # Extract the first two elements 'a' and 'b' from the sequence using extended unpacking.
    a, b, *sequence = sequence
    
    # Initialize a variable 'skipped' to keep track of the number of skipped elements.
    skipped = 0

    # Iterate through the remaining elements 'c' in the sequence.
    for c in sequence:
        if a < b < c:  # Check if the current subsequence is in increasing order (e.g., 1 < 2 < 3).
            a, b = b, c  # Update 'a' and 'b' for the next comparison and continue.
            continue
        elif b < c:    # Check if the current subsequence has two increasing elements and one out of order (e.g., 1 < 2, but 2 < 0).
            a, b = b, c  # Update 'a' and 'b' for the next comparison.
        elif a < c:    # Check if the current subsequence has one increasing element and two out of order (e.g., 1 < 0, but 0 < 3).
            a, b = a, c  # Update 'a' for the next comparison.
        skipped += 1  # Increment the 'skipped' count to track the number of skipped elements.
        if skipped == 2:  # If two or more elements have been skipped, return False.
            return False
    return a < b  # Check if the final 'a' and 'b' form an increasing subsequence.

# Test cases to check the behavior of the 'almost_increasing_sequence' function.
print(almost_increasing_sequence([]))
print(almost_increasing_sequence([1]))
print(almost_increasing_sequence([1, 2]))
print(almost_increasing_sequence([1, 2, 3]))
print(almost_increasing_sequence([3, 1, 2]))
print(almost_increasing_sequence([1, 2, 3, 0, 4, 5, 6]))
print(almost_increasing_sequence([1, 2, 3, 0]))
print(almost_increasing_sequence([1, 2, 0, 3]))
print(almost_increasing_sequence([10, 1, 2, 3, 4, 5]))
print(almost_increasing_sequence([1, 2, 10, 3, 4]))
print(almost_increasing_sequence([1, 2, 3, 12, 4, 5]))
print(almost_increasing_sequence([3, 2, 1]))
print(almost_increasing_sequence([1, 2, 0, -1]))
print(almost_increasing_sequence([5, 6, 1, 2]))
print(almost_increasing_sequence([1, 2, 3, 0, -1]))
print(almost_increasing_sequence([10, 11, 12, 2, 3, 4, 5])) 

Sample Output:

True
True
True
True
True
True
True
True
True
True
True
False
False
False
False
False

Flowchart:

Python Code Editor:

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