edgelord N tasks topological sorting

topo.py

# "There's a set of N tasks, from which some have to be done before the other. The order is described by a 2D array T[N][N]. If T[a][b] = 1, then the task 'a' has to be done before the task 'b'. In the case of T[a][b] = 2, the task b has to be done earlier, and when T[a][b] = 0 the order doesn't matter. Implement a function tasks(T), which for the given array T returns an array with the tasks in the order of execution."
# Example:  For the array T = [ [0,2,1,1], [1,0,1,1], [2,2,0,1], [2,2,2,0] ] the result is [1,0,2,3]

# an arbitrary array (because there can be more than one solution to a particular graph)

T = [ [0,2,1,1], [1,0,1,1], [2,2,0,1], [2,2,2,0] ]

import sys

v = len(T) # square matrix

m = {} # adj list in a recursively traversable way

for i in range(v):
    m[i] = set()

empty_graph = True
for i in range(v):
    for j in range(v):
        empty_graph = False
        if T[i][j] == 1: # a has to be done before b
            m[i].add(j)
        elif T[i][j] == 2:
            m[j].add(i)

if empty_graph: # special case: no edges at all whatsoever!
    for i in range(v):
        print(i)
    sys.exit()

ans = []

visited = set()
def dfs(v):
    visited.add(v)
    for next_vertex in m[v]:
        if next_vertex not in visited:
            dfs(next_vertex)
        
    ans.append(v)

def topological_sort():
    for vertex in m.keys():
        if vertex not in visited:
            dfs(vertex)
        
topological_sort()
print(ans[::-1])