Reconstruct a 2-Row Binary Matrix — LeetCode 1253 Python Solution

The problem

Given the following details of a matrix with n columns and 2 rows : The matrix is a binary matrix, which means each element in the matrix can be 0 or 1. The sum of elements of the 0-th(upper) row is given as upper.

Example

Input

upper = 2, lower = 1, colsum = [1,1,1]

Output

[[1,1,0],[0,0,1]]

Explanation

[[1,0,1],[0,1,0]], and [[0,1,1],[1,0,0]] are also correct answers.

Python solution

class Solution:
    def reconstructMatrix(
        self, upper: int, lower: int, colsum: List[int]
    ) -> List[List[int]]:
        n = len(colsum)
        ans = [[0] * n for _ in range(2)]
        for j, v in enumerate(colsum):
            if v == 2:
                ans[0][j] = ans[1][j] = 1
                upper, lower = upper - 1, lower - 1
            if v == 1:
                if upper > lower:
                    upper -= 1
                    ans[0][j] = 1
                else:
                    lower -= 1
                    ans[1][j] = 1
            if upper < 0 or lower < 0:
                return []
        return ans if lower == upper == 0 else []

Complexity

Pattern: Matrix and Grid

Treat a 2-D grid as a graph whose neighbours are the four adjacent cells. LeetCode 1253. Reconstruct a 2-Row Binary Matrix is filed here because LeetCode tags it Matrix, which is the vocabulary this hub collects.

The matrix and grid guide has the Python template for the pattern and the 216 LeetCode problems that use it.

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