Pair sort

import sys 

input = sys.stdin.read().split()

n = int(input[0])
a = [int(x) for x in input[1:]]

idx = [[] for _ in range(n+1)]
for i,val in enumerate(a) :
    idx[val].append(i)

steps = []

for i in range(n):
    p1 = 2*i
    p2 = 2*i +1

    if a[p1] == a[p2]:
        continue

    x = a[p1]
    y = a[p2]
    
    p3 = idx[x][1] if idx[x][0] == p1 else idx[x][0]

    steps.append((p2+1,p3+1))
    a[p2], a[p3] = a[p3], a[p2]

    if idx[y][0] == p2 :
        idx[y][0] = p3 
    else : 
        idx[y][1] = p3




print(len(steps))
for s in steps : 
    print(f"{s[0]} {s[1]}")

Test 1

Verdict: ACCEPTED

Test 2

Verdict: ACCEPTED

Test 3

Verdict: ACCEPTED

Test 4

Verdict: ACCEPTED

Test 5

Verdict: ACCEPTED

Test 6

Verdict: ACCEPTED

Test 7

Verdict: ACCEPTED

Test 8

Verdict: ACCEPTED

Test 9

Verdict: ACCEPTED

Test 10

Verdict: ACCEPTED

Test 11

Verdict: ACCEPTED

Test 12

Verdict: ACCEPTED

Test 13

Verdict: ACCEPTED

Test 14

Verdict: ACCEPTED