Sum of Three Values

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

#define cin(vec) for(auto& i : vec) cin >> i
#define cin_2d(vec, n, m) for(int i = 0; i < n; i++) for(int j = 0; j < m && cin >> vec[i][j]; j++);
#define cout(vec) for(auto& i : vec) cout << i << " "; cout << "\n";
#define cout_2d(vec, n, m) for(int i = 0; i < n; i++, cout << "\n") for(int j = 0; j < m && cout << vec[i][j] << " "; j++);
#define cout_map(mp) for(auto& [f, s] : mp) cout << f << "  " << s << "\n";
#define Time cerr << "Time Taken: " << (float)clock() / CLOCKS_PER_SEC << " Secs" << "\n";
#define fixed(n) cout << fixed << setprecision(n)
#define ceil(n, m) (((n) / (m)) + ((n) % (m) ? 1 : 0))
#define fill(vec, value) memset(vec, value, sizeof(vec));
#define Num_of_Digits(n) ((int)log10(n)+1)
#define all(vec) vec.begin(),vec.end()
#define rall(vec) vec.rbegin(),vec.rend()
#define sz(x) int(x.size())
#define fi first
#define se second
#define Pair pair < int, int >
#define ll long long
#define ull unsigned long long
#define Mod  1'000'000'007
#define INF 2'000'000'000
#define PI acos(-1)

void Code_Crush(){
  ios_base::sync_with_stdio(false), cin.tie(nullptr), cout.tie(nullptr);
  #ifndef ONLINE_JUDGE
    freopen("input.txt", "r", stdin), freopen("output.txt", "w", stdout);
  #endif
}

int main(){
  Code_Crush();
  int n, target1;                            cin >> n >> target1;
  vector < int > nums(n);
  cin(nums);
  vector < pair < int, int > > idx;
  for(int i = 0; i < nums.size(); i++)
      idx.push_back({nums[i], i});
  sort(idx.begin(), idx.end());
  for(int i = 0; i < n; i++){
    int target = target1 - nums[i];
    int l = 0, r = nums.size() - 1;
    while(l < r){
        if(i == idx[l].se) l++;
        else if(i == idx[r].se) r--;
        else {
          if(idx[l].first + idx[r].first == target){
           return cout << idx[l].second + 1 << " " << idx[r].second + 1 << " " << i + 1, 0;
          }
          (idx[l].first + idx[r].first > target ? r-- : l++);
        }
    }
  }
  cout << "IMPOSSIBLE";
  Time
  return 0;
}