3SUM

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.util.Arrays;
import java.util.StringTokenizer;

public class ThreeSum {
    public static void main(String[] args) {
        FastScanner input = new FastScanner(System.in);
        int n = input.nextInt();
        int x = input.nextInt();

        int[] numbers = new int[n];

        for (int i = 0; i < n; i++){
            numbers[i] = input.nextInt();
        }
        int[] sorted = numbers.clone();
        Arrays.sort(sorted);

        int i = 0;
        int j = 0;
        int k = 0;

        Boolean found = false;
        while(i < n-2 && !found){

            j = i+1;
            k =n-1;
            while (k > j && !found && j<n){
                if (sorted[i] + sorted[j] + sorted[k] > x) {
                    k--;
                } else if (sorted[i] + sorted[j] + sorted[k] < x){
                    j++;
                } else {
                    found = true;
                    i--;
                }
            }
            i++;
        }


            int a = sorted[i];
            int b = sorted[j];
            int c = sorted[k];

            int aI = 0;
            int bI = 0;
            int cI = 0;

            for (int y = 0; y < n; y++){
                if(numbers[y] == a && aI == 0){
                    aI = y+1;
                } else if (numbers[y] == b && bI == 0){
                    bI = y+1;
                } else if (numbers[y] == c && cI == 0){
                    cI = y +1;
                }
            }

            if (!found || aI == 0|| bI == 0|| cI == 0){
                System.out.println("IMPOSSIBLE");
            }else {
                System.out.println(aI + " " + bI + " " + cI);
            }


    }

    static class FastScanner { //static class fastScanner
    private BufferedReader reader = null;
    private StringTokenizer tokenizer = null;

    public FastScanner(InputStream in) {
        reader = new BufferedReader(new InputStreamReader(in));
        tokenizer = null;
    }

    public String next() {
        if (tokenizer == null || !tokenizer.hasMoreTokens()) {
            try {
                tokenizer = new StringTokenizer(reader.readLine());
            } catch (IOException e) {
                throw new RuntimeException(e);
            }
        }
        return tokenizer.nextToken();
    }

    public String nextLine() {
        if (tokenizer == null || !tokenizer.hasMoreTokens()) {
            try {
                return reader.readLine();
            } catch (IOException e) {
                throw new RuntimeException(e);
            }
        }

        return tokenizer.nextToken("\n");
    }

    public long nextLong() {
        return Long.parseLong(next());
    }

    public int nextInt() {
        return Integer.parseInt(next());
    }

    public double nextDouble() {
    	 return Double.parseDouble(next());
	 }

    public int[] nextIntArray(int n) {
        int[] a = new int[n];
        for (int i = 0; i < n; i++)
            a[i] = nextInt();
        return a;
    }

    public long[] nextLongArray(int n) {
        long[] a = new long[n];
        for (int i = 0; i < n; i++)
            a[i] = nextLong();
        return a;
    }
}
}

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