1253. Reconstruct a 2-Row Binary Matrix

Problem Link

Description

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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.
• The sum of elements of the 1-st(lower) row is given as lower.
• The sum of elements in the i-th column(0-indexed) is colsum[i], where colsum is given as an integer array with length n.

Your task is to reconstruct the matrix with upper, lower and colsum.

Return it as a 2-D integer array.

If there are more than one valid solution, any of them will be accepted.

If no valid solution exists, return an empty 2-D array.

 

Example 1:

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.

Example 2:

Input: upper = 2, lower = 3, colsum = [2,2,1,1]
Output: []

Example 3:

Input: upper = 5, lower = 5, colsum = [2,1,2,0,1,0,1,2,0,1]
Output: [[1,1,1,0,1,0,0,1,0,0],[1,0,1,0,0,0,1,1,0,1]]

 

Constraints:

• 1 <= colsum.length <= 10^5
• 0 <= upper, lower <= colsum.length
• 0 <= colsum[i] <= 2

Solution

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Python3

class Solution:
    def reconstructMatrix(self, upper: int, lower: int, colsum: List[int]) -> List[List[int]]:
        cols = len(colsum)
        
        res = [[0]*cols for _ in range(2)]
        
        for j in range(cols):
            if colsum[j] == 2:
                res[0][j] = 1
                res[1][j] = 1
                colsum[j] -= 2
                upper -= 1
                lower -= 1
            
            if upper < 0 or lower < 0: return []
        
        
        for i in range(2):
            for j in range(cols):
                rowsum = upper if i == 0 else lower
 
                if rowsum > 0 and colsum[j] > 0:
                    res[i][j] = 1
                
                    if i == 0: upper -= 1
                    else: lower -= 1
 
                    colsum[j] -= 1
                
 
        return res if upper + lower + sum(colsum) == 0 else []