Leetcode "Set Matrix zeroes" Python implementation

title :

Given a m x n Matrix, if an element was 0, set its entire row and column to 0. Do it on 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 is not the best solution.
Could you devise a constant space solution?

Code: OJ tested via runtime:220 MS

1 classSolution:2     #@param Matrix, a list of lists of integers3     #RETURN Nothing, MODIFY matrix in place.4     defsetzeroes (self, matrix):5         #None case6         ifMatrix isNone:7             returnNone8         #dimension of the matrix9ROW =len (Matrix)TenCOL =Len (matrix[0]) One         #record the status of first row and first column AFirst_row_contains_zero =False -          forIinchRange (COL): -             ifMatrix[0][i] = =0: theFirst_row_contains_zero =True -First_col_contains_zero =False -          forIinchRange (ROW): -             ifMatrix[i][0] = =0: +First_col_contains_zero =True -         #visit the row-1xcol-1 matrix and check zeros +          forRowinchRange (1, ROW): A              forColinchRange (1, COL): at                 ifMatrix[row][col] = =0: -Matrix[row][0] =0 -Matrix[0][col] =0 -         #set zero rows and zero columns -          forRowinchRange (1, ROW): -              forColinchRange (1, COL): in                 ifMatrix[row][0]==0ormatrix[0][col]==0: -Matrix[row][col] =0 to         ifFirst_row_contains_zero: +              forIinchRange (COL): -Matrix[0][i] =0 the         ifFirst_col_contains_zero: *              forIinchRange (ROW): $Matrix[i][0] = 0

Ideas :

The difficulty of the topic is to require the use of constant space.

The method is to first record whether the first and first rows of the matrix contain 0 elements, and then use the first and first columns as the remaining columns and rows to contain 0 of the record positions, thus saving O (m+n) space.

Here's a stem to be explained:

For example Matrix[0][j] as the Matrix J column contains 0 of the flag, there are two cases:

1. Matrix[0][j] itself is 0, the elements of the entire J column (including Matrix[0][j]) are finally 0

2. Matrix[0][j] is nonzero if the remaining elements of J column have 0, then Matrix[0][j] is 0, and if the remaining elements of J column do not contain 0, then Matrix[0][j] remains the original value and is not zero.

After the same trick, you can write the code out of AC.

Learn the following logs mainly:

Http://blog.sina.com.cn/s/blog_45b8132001018xie.html

In addition, incompatible, the first version of the code to write their own also attached.

OJ Test via runtime:213 ms

classSolution:#@param Matrix, a list of lists of integers    #RETURN Nothing, MODIFY matrix in place.    defsetzeroes (self, matrix):#None case        ifMatrix isNone:returnNone#dimension of the matrixROW =len (matrix) COL=Len (matrix[0])#record zero rows and zero columnsZero_row = [False forIinchrange (ROW)] Zero_col= [False forIinchrange (COL)] forRowinchRange (ROW): forAo.inchRange (COL):ifMatrix[row][col] = =0:zero_row[row]=True Zero_col[col]=True#set zero rows and zero columns         forRowinchRange (ROW): forColinchRange (COL):ifZero_row[row]orZero_col[col]: Matrix[row][col]= 0

It feels like the two kinds of code are almost as efficient. It's just a matter of time and space swaps.

However, since only a small sacrifice of time, there is some space, is also good, in the future can be remembered in the work of this trick.

Leetcode "Set Matrix zeroes" Python implementation