3SUM

def two_sum(a, target):
    left, right = 0, len(a) - 1

    while left < right:
        sum = a[left][0] + a[right][0]

        if sum == target:
            return a[left][1], a[right][1]
        elif sum < target:
            left += 1
        else:
            right -= 1

    return False

n, x = map(int, input().split())
a = list(map(int, input().split()))
printed = False
b = [(a[i], i) for i in range(n)]
b.sort()

for i in range(n):
    ans = two_sum(b[i + 1:], x - b[i][0])
    if ans:
        l, r = ans
        print(b[i][1] + 1, l + 1, r + 1)
        printed = True
        break

if not printed:
    print('IMPOSSIBLE')

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

Test 15

Verdict: ACCEPTED

Test 16

Verdict: ACCEPTED

Test 17

Verdict: ACCEPTED

Test 18

Verdict: ACCEPTED

Test 19

Verdict: ACCEPTED

Test 20

Verdict: ACCEPTED

Test 21

Verdict: ACCEPTED

Test 22

Verdict: ACCEPTED

Test 23

Verdict: ACCEPTED