卖萌的弱渣

I am stupid, I am hungry.

Set Matrix Zeroes

Given a m x n matrix, if an element is 0, set its entire row and column to 0. Do it in place.

click to show follow up.

Follow up:

  • Did you use extra space?
  • A straight forward solution using O(mn) space is probably a bad idea.
  • A simple improvement uses O(m + n) space, but still not the best solution.
  • Could you devise a constant space solution?

Solution

  • Reuse the first row and first column to store the flag for the following rows and folumns
(Set-Matrix-Zeroes.py) download
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class Solution(object):
    def setZeroes(self, matrix):
        """
        :type matrix: List[List[int]]
        :rtype: void Do not return anything, modify matrix in-place instead.
        """

        if not matrix:
            return

        fr = False
        fc = False

        row = len(matrix)
        col = len(matrix[0])

        # check first col
        for i in range(row):
            if matrix[i][0] == 0:
                fc = True
                break

        # check first row
        for i in range(col):
            if matrix[0][i] == 0:
                fr = True
                break

        # use first row and col to store the status of other rows/cols
        for i in range(1,row):
            for j in range(1,col):
                if matrix[i][j] == 0:
                    matrix[i][0] = 0
                    matrix[0][j] = 0

        # update row/col except first row/col
        for i in range(1,row):
            if matrix[i][0] == 0:
                for j in range(1,col):
                    matrix[i][j] = 0

        for i in range(1,col):
            if matrix[0][i] == 0:
                for j in range(1,row):
                    matrix[j][i] = 0

        # update the first row/col
        if fr:
            for i in range(0,col):
                matrix[0][i] = 0
        if fc:
            for i in range(0,row):
                matrix[i][0] = 0
        return