Connect cities

line = input()
parts = line.split(" ")
cities = int(parts[0])
roads = int(parts[1])

adj: dict[int, set[int]] = {}

for i in range(0, roads):
    line = input()
    parts = line.split(" ")
    city1 = int(parts[0])
    city2 = int(parts[1])

    if city1 in adj:
        adj[city1].add(city2)
    else:
        adj[city1] = set([city2])
    if city2 in adj:
        adj[city2].add(city1)
    else:
        adj[city2] = set([city1])


for i in range(1, cities + 1):
    if i not in adj:
        adj[i] = set()

seen: set[int] = set([])


def dfs(city: int):
    if city in seen:
        return
    seen.add(city)
    if city in adj:
        for city in adj[city]:
            dfs(city)


unique: list[int] = []

for city in adj:
    if not (city in seen):
        unique.append(city)
    dfs(city)

new_roads: list = []

for i in range(0, len(unique) - 1):
    new_roads.append((unique[i], unique[i + 1]))

print(len(new_roads))

for a, b in new_roads:
    print(f"{a} {b}")

Test 1

Verdict: ACCEPTED

Test 2

Verdict: ACCEPTED

Test 3

Verdict: ACCEPTED

Test 4

Verdict: ACCEPTED

Test 5

Verdict: ACCEPTED

Test 6

Verdict: RUNTIME ERROR

Traceback (most recent call last):
  File "/box/input/code.py", line 45, in <module>
    d...

Test 7

Verdict: RUNTIME ERROR

Traceback (most recent call last):
  File "/box/input/code.py", line 45, in <module>
    d...

Test 8

Verdict: RUNTIME ERROR

Traceback (most recent call last):
  File "/box/input/code.py", line 45, in <module>
    d...

Test 9

Verdict: RUNTIME ERROR

Traceback (most recent call last):
  File "/box/input/code.py", line 45, in <module>
    d...

Test 10

Verdict: RUNTIME ERROR

Traceback (most recent call last):
  File "/box/input/code.py", line 45, in <module>
    d...

Test 11

Verdict: ACCEPTED

Test 12

Verdict: ACCEPTED