3SUM

import sys

def main():
    input_data = sys.stdin.read().split()
    
    n = int(input_data[0])
    target = int(input_data[1])
    arr = [int(x) for x in input_data[2:]]

    pair_sums = {}

    for i in range(n):
        x = arr[i]
        needed = target - x

        if needed in pair_sums:
            idx1, idx2 = pair_sums[needed]
            print(f"{idx1} {idx2} {i + 1}")
            return

        for j in range(i):
            current_pair_sum = arr[j] + x
            if current_pair_sum < target and current_pair_sum not in pair_sums:
                pair_sums[current_pair_sum] = (j + 1, i + 1)

    print("IMPOSSIBLE")

main()

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: TIME LIMIT EXCEEDED

Test 18

Verdict: ACCEPTED

Test 19

Verdict: ACCEPTED

Test 20

Verdict: ACCEPTED

Test 21

Verdict: TIME LIMIT EXCEEDED

Test 22

Verdict: ACCEPTED

Test 23

Verdict: ACCEPTED