3SUM

input/code.cpp: In function 'int main()':
input/code.cpp:17:32: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   17 |                 for (int j=0; j<aa.size(); j++) {
      |                               ~^~~~~~~~~~
input/code.cpp:25:40: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   25 |                         for (int i=0; i<aa.size(); i++) {
      |                                       ~^~~~~~~~~~

#include <bits/stdc++.h>
using namespace std;

set<int> aas;
vector<int> aa;
map<int, pair<int, int>> mm;
map<int, int> qq;

int main() {
	int n, x;
	cin >> n >> x;
	for (int i=0; i<n; i++) {
		int a;
		cin >> a;
		aas.insert(a);
		aa.push_back(a);
		for (int j=0; j<aa.size(); j++) {
			if (j == i) continue;
			mm[(aa[j]+aa[i])] = make_pair(j, i);
		}
	}
	for (auto [a, p] : mm) {
		if (aas.count(x-a)) {
			int li = -1;
			for (int i=0; i<aa.size(); i++) {
				if (i != p.first && i != p.second && aa[i] == x-a) {
					li = i;
					break;
				}
			}
			if (li == -1) continue;
			cout << p.first+1 << " " << p.second+1 << " " << li+1 << endl;
			return 0;
		}
	}
	
	cout << "IMPOSSIBLE" << endl;
	return 0;
}

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: TIME LIMIT EXCEEDED

Test 13

Verdict: ACCEPTED

Test 14

Verdict: ACCEPTED

Test 15

Verdict: ACCEPTED

Test 16

Verdict: TIME LIMIT EXCEEDED

Test 17

Verdict: TIME LIMIT EXCEEDED

Test 18

Verdict: ACCEPTED

Test 19

Verdict: ACCEPTED

Test 20

Verdict: TIME LIMIT EXCEEDED

Test 21

Verdict: TIME LIMIT EXCEEDED

Test 22

Verdict: ACCEPTED

Test 23

Verdict: ACCEPTED