109D - Lucky Sorting - CodeForces Solution

def check(x):
    return all(digit not in str(x) for digit in "01235689")

def change(a, b):
    x, y = rpos[a], rpos[b]
    if x == y:
        return 1
    res.append((x + 1, y + 1))
    rpos[pos[x]], rpos[pos[y]] = rpos[pos[y]], rpos[pos[x]]
    pos[x], pos[y] = pos[y], pos[x]
    return 1

n = int(input())
a = list(map(int, input().split()))
b = [(a[i], i) for i in range(n)]
pos = [i for i in range(n)]
rpos = [i for i in range(n)]
b.sort()
res = []
id = -1
ok = 1

for i in range(n):
    if i != b[i][1]:
        ok = 0
    if id == -1 and check(a[i]):
        id = i

if ok == 1:
    print(0)
    exit(0)

if ok == 0 and id == -1:
    print(-1)
    exit(0)

for i in range(n):
    index = b[i][1]
    if id == index:
        continue
    change(pos[i], id)
    change(id, index)

print(len(res))
for x, y in res:
    print(x, y)