73 Set Matrix Zeroes

Given amxnmatrix, if an element is 0, set its entire row and column to 0. Do it in place.

click to show follow up.

Complexity: O(n) time and space

The Idea: Not O(1) space, but other wise minimally efficient. We store the rows and cols of the located zeros into sets, as to avoid iterating through rows and columns that are going to be zeroed out anyway.

class Solution:
    def setZeroes(self, matrix):
        """
        :type matrix: List[List[int]]
        :rtype: void Do not return anything, modify matrix in-place instead.
        """
        row_s = len(matrix)
        col_s = len(matrix[0])

        set_r = set()
        set_c = set()

        for i in range(row_s):
            for j in range(col_s):
                if (matrix[i][j] == 0):
                    set_r.add(i)
                    set_c.add(j)
            j = 0

        # zero out the rows
        for r in set_r:
            matrix[r] = [0] * col_s

        # zero out the cols
        for c in set_c:
            for iter in range(0, row_s):
                matrix[iter][c] = 0

Testing

obj = Solution()

matrix = [[1,2,3],
          [4,5,0],
          [8,9,10]]

obj.setZeroes(matrix)
print(matrix)

matrix2 = [[0,2,3],
          [4,5,6],
          [8,9,0]]

obj.setZeroes(matrix2)
print(matrix2)

matrix3 = [[0,1]]

obj.setZeroes(matrix3)
print(matrix3)

matrix4 = [[1], 
           [0]]

obj.setZeroes(matrix4)
print(matrix4)