3SUM

input/code.cpp: In function 'void Test()':
input/code.cpp:19:12: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   19 |     freopen("temp\\in.txt", "r", stdin);
      |     ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~

#include<bits/stdc++.h>
using namespace std;
typedef long long LL;
const int N=5005;

struct Node
{
    int v, x;
    Node(int v_=0, int x_=0):
        v(v_), x(x_) {}
    bool operator < (const Node& node_)const {
        return v < node_.v;
    }
}nodes[N];


void Test()
{
    freopen("temp\\in.txt", "r", stdin);
}
int main()
{
    // Test();
    int n, sum, temp;
    cin >> n >> sum;

    for(int i=1; i<=n; i++)
    {
        cin >> temp;
        nodes[i] = Node(temp, i);
    }
    sort(nodes+1, nodes+n+1);
    for(int i=1; i<=n; i++)
    {
        Node &node = nodes[i];
        if(node.v > sum) break;
        if(node.v == nodes[i-1].v) continue;

        int low = i+1, high = n;

        while(low < high)
        {
            int sum_ = node.v + nodes[low].v + nodes[high].v;

            if(sum_ == sum) {
                cout << node.x << " " << nodes[low].x << " " << nodes[high].x;
                return 0;
            } else if(sum_ < sum) {
                low++;
            } else {
                high--;
            }
        }
    }
    cout << "IMPOSSIBLE";
    

    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: 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