Pair sort

def solve():
    n = int(input())
    arr = list(map(int, input().split()))
    from collections import defaultdict

    positions = defaultdict(list)
    for idx, val in enumerate(arr):
        positions[val].append(idx)

    swaps = []
    pivot = arr[0]  
    skip_pivot = False

    for i in range(0, 2 * n, 2):
        x = arr[i]
        if arr[i + 1] == x:
            continue
        else:
            if not skip_pivot and x == pivot:
                skip_pivot = True
                continue
            idx_list = positions[x]
        
            if idx_list[0] == i:
                other_index = idx_list[1]
            else:
                other_index = idx_list[0]

            val_i1 = arr[i + 1]
            val_other = arr[other_index]

            arr[i + 1], arr[other_index] = arr[other_index], arr[i + 1]
            swaps.append((i + 2, other_index + 1))  

            positions[val_other].remove(other_index)
            positions[val_other].append(i + 1)
            positions[val_i1].remove(i + 1)
            positions[val_i1].append(other_index)

    print(len(swaps))
    for swap in swaps:
        print(swap[0], swap[1])
solve()

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