3SUM

import sys
from collections import deque, defaultdict, Counter
from heapq import heappush, heappop, heapify
from bisect import bisect_left, bisect_right
from itertools import permutations, combinations, product, accumulate, groupby
from functools import lru_cache, cmp_to_key, reduce
from math import gcd, isqrt, comb, inf, pi, sqrt, atan2, hypot


def main():
    data = sys.stdin.buffer.read().split(); idx = 0
    # n = int(data[idx]); idx += 1
    n, x = map(int, data[idx:idx + 2]); idx += 2
    a = list(map(int, data[idx:idx + n])); idx += n
    # s = data[idx].decode(); idx += 1                  # strings

    # for _ in range(m):
    #     a, b = map(int, data[idx:idx + 2]); idx += 2

    # g = [data[idx + i].decode() for i in range(n)]; idx += n  # grid of n rows, no spaces, strings

    # input = sys.stdin.readline
    # n, m = map(int, input().split())
    # s = input().strip()  # strip removes the trailing newline
    # for line in sys.stdin:  # read until EOF

    out = []

    # a.sort()
    numbers = {}
    for num in a:
        numbers[num] = numbers.get(num, 0) + 1



    for i in range(len(a)):
        for j in range(i+1,len(a)):
            remaining = x - (a[i] + a[j])
            # if remaining >= 0

            count = numbers.get(remaining, 0)
            if a[i] == remaining:
                count -= 1
            if a[j] == remaining:
                count -= 1



            if count > 0:
                a[i] = -1
                a[j] = -1
                new_num_idx = a.index(remaining)  + 1
                # print(f"index of {remaining} is {new_num_idx} and count is {count}")
                print(i+1, j+1, new_num_idx)


                return

    print("IMPOSSIBLE")


    # sys.stdout.write("\n".join(map(str, out)) + "\n")  # one value per line
    # print(*out)                                      # space separated on one line
    # print(f"{ans:.6f}")                              # float with 6 decimals
    # print("\n".join("".join(row) for row in g))      # grid of chars


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: 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