Connect cities

n,m = [int(x) for x in input().split()]
voisin = [[] for _ in range (n)]
atteignable = [False for i in range(n)]
atteignable[0] = True

for i in range (m):
    a,b = [int(x)-1 for x in input().split()]
    voisin[a].append(b)
    voisin[b].append(a)

def lier_ville(ville):
    atteignable[ville]=True
    for city in voisin[ville]:
        if atteignable[city] == False:
            lier_ville(city)



lier_ville(0)
i = 1
chemin_a_creer = []
while i<n:
    if atteignable[i] == False:
        atteignable[i] = True
        lier_ville(i)
        chemin_a_creer.append("1 "+ str(i+1))
        i+=1
    else :
        i+=1

print(len(chemin_a_creer))
for elmt in chemin_a_creer:
    print(elmt)

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 "input/code.py", line 25, in <module>
    lier_v...

Test 7

Verdict: RUNTIME ERROR

Traceback (most recent call last):
  File "input/code.py", line 25, in <module>
    lier_v...

Test 8

Verdict: RUNTIME ERROR

Traceback (most recent call last):
  File "input/code.py", line 19, in <module>
    lier_v...

Test 9

Verdict: RUNTIME ERROR

Traceback (most recent call last):
  File "input/code.py", line 19, in <module>
    lier_v...

Test 10

Verdict: RUNTIME ERROR

Traceback (most recent call last):
  File "input/code.py", line 19, in <module>
    lier_v...

Test 11

Verdict: ACCEPTED

Test 12

Verdict: ACCEPTED