Diagonals in North East Direction - Time Limit Exceeded in Python 3.8.3 - python-3.x

Question

The program must accept an integer matrix of size RxC as the input. The program must print the integers in the diagonals in the North-East directions of the matrix in the seprate line as output.
Boundary:
2<=R,C<=100
Time Limit : 500ms
Example 1:
Input:
3 3
73 77 76
71 17 87
37 73 98
Output:
73
71 77
37 17 76
73 87
98
Example 2:
Input:
4 6
97 78 7 39 92 45
68 100 49 95 97 100
59 41 81 22 26 100
46 37 81 12 93 10
Output:
97
68 78
59 100 7
46 41 49 39
37 81 95 92
81 22 97 45
12 26 100
93 100
10
My Code:
row,col = map(int,input().split())
matrix = [list(map(int,input().split())) for i in range(row)]
# Redundancy of row and col
rep = []
for i in range(row):
for j in range(col):
b = []
for k in range(i,row):
if (j,k) not in rep:
b.append(matrix[k][j])
rep.append((j,k))
j-=1
if j<0:break
if len(b):print(*(b[::-1]))
My code works well but when the matrix is of size (100,100) it exceeds the given time limit, is there a way to reduce it. Thanks in advance
Note : No External Libraries should be used!

Answer 1

The trick here is to realize that because each number only appears in the solution once, so we really only need to evaluate each value once.
We can also see that each matrix will result in row + col - 1 number of North-East direction diagonals, which will help us.
# Original code
row,col = map(int,input().split())
# I won't turn them into ints, strings actually make it easier for my work
matrix = [input().split() for i in range(row)]
diagonals = [""] * (row + col - 1)
for i in range(row):
for j in range(col):
# determine which diagonal the number belongs to, and prepend it
diagonals[i + j] = "%s %s" % (matrix[i][j], diagonals[i + j])
# print out diagonals one at a time
for diagonal in diagonals: print(diagonal)
I never got the chance to run it, but this should give the general idea!
(new to SO, plz be nice :D)