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75 matches

Set Matrix Zeroes in Python: Markers List Grid Demo

Given a matrix, this code finds all rows and columns that contain a zero and sets every element in those rows and columns to zero, using boolean marker arrays.

matrix arrays algorithm

Python

def set_zeroes(matrix):
    rows, cols = len(matrix), len(matrix[0])
    row_markers = [False] * rows
    col_markers = [False] * cols

    # First pass: record which rows and columns contain zeros
    for i in range(rows):
        for j in range(cols):
            if matrix[i][j] == 0:
                row_markers[i] …

14 0 Open

Algorithms & data structures easy

Sort list by multiple keys with tuple ordering in Python

Sort a list of dictionaries by multiple criteria — surname, age, then score descending — using a tuple key and negation.

sorting tuples lambda

Python

def sort_multi_key(data):
    # Sorts by surname, then age, then score descending
    return sorted(
        data,
        key=lambda person: (
            person['surname'].lower(),
            person['age'],
            -person['score']  # negative to reverse sort by score
        )
    )


if __name__ == "__main__"…

14 0 Open

Algorithms & data structures easy

Stable merge two lists by custom comparator in Python

Merge two lists into one sorted output using a custom comparator while maintaining the original order of equal elements.

merge stable-sort custom-comparator

Python

from functools import cmp_to_key

def compare(x, y):
    # Custom comparator: sorts by length first, then by original index for stability
    if len(x) != len(y):
        return len(x) - len(y)
    return 0  # Equal keys preserve original order (stable)

def merge_stable(left, right, cmp_func):
    result = []
    i =…

13 0 Open

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