Shared code

/*
  author: @ankingcodes
  created: 2021-07-15 13:45:44.426881
*/
        
#include<bits/stdc++.h>
#include<algorithm>
#include<ext/pb_ds/assoc_container.hpp>
#include<ext/pb_ds/tree_policy.hpp>

using namespace __gnu_pbds;
using namespace std;
#define ll long long
#define mod 1000000007

typedef tree<int, null_type, less<int>, rb_tree_tag,
                tree_order_statistics_node_update> pbds;

typedef tree<pair<int, int>, null_type, less<pair<int, int>>, rb_tree_tag,
                tree_order_statistics_node_update> pairpbds;

int main(){
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  ll n, k; cin>>n>>k;  
  vector<pair<ll, ll>> a;
  for (int i=0;i<n;i++) {
    ll x; cin >> x;
    a.push_back({ x, i });
  }
  sort(begin(a), end(a));
  int l=0, r=n-1;
  bool flag = false;
  while(l < r) { 
    ll sum = a[l].first + a[r].first;
    if (sum == k) {
      flag = true;
      break;
    } else if (sum < k) l++;
    else r--;
  }
  if (flag) cout << a[l].second+1 << " " << a[r].second+1 << endl;
  else cout << "IMPOSSIBLE";
  return 0;
}