3SUM

#include <stdint.h>
#include <stdlib.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stdbool.h>

typedef struct {
    uint64_t v;
    uint64_t i;
} pair;

typedef struct {
    uint64_t v;
    uint64_t i1;
    uint64_t i2;
} triple;

int comp(const void *a, const void *b){
    pair *ra = (pair*) a;
    pair *rb = (pair*) b;
    if (ra->v < rb->v)
        return -1;
    if (ra->v > rb->v)
        return 1;
    return 0;
}


int main() {
    uint64_t n = 0;
    uint64_t x = 1;
    if (scanf("%ld %ld", &n, &x) == 0)
        return EXIT_FAILURE;

    if (n < 3){
        printf("IMPOSSIBLE");
        exit(EXIT_SUCCESS);
    }


    uint64_t *values = (uint64_t*) malloc(n * sizeof(uint64_t));
    pair *sorted = (pair*) malloc(n * sizeof(pair));

    uint64_t tmp;
    for (uint64_t i = 0; i < n; i++){
        if (scanf("%ld", &tmp) == 0)
            return EXIT_FAILURE;
        sorted[i] = {tmp, i};
        values[i] = tmp;
    }
    qsort(sorted, n, sizeof(pair), &comp);

    for (uint64_t i = 0; i < n-2; i++){
        uint64_t k = n-1;
        // printf("k = n-1 = %ld\n", k);
        for (uint64_t j = i+1; j < n-1; j++){
            while ( x < sorted[k].v + sorted[i].v + sorted[i].v && k > j){
                k--;
                // printf("k--=%ld\n", k);
            }
            // printf("j=%ld\n", j);
            if (k<=j){
                break;
            }
            // printf("3sum=%ld\n", sorted[i].v + sorted[i].v + sorted[k].v);
            if (x == sorted[i].v + sorted[j].v + sorted[k].v){
                printf("%ld %ld %ld\n", 1+sorted[i].i, 1+sorted[j].i, 1+sorted[k].i);
                exit(EXIT_SUCCESS);
            }
        }
    }
    printf("IMPOSSIBLE");


    // main algo


    return EXIT_SUCCESS;
}

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: WRONG ANSWER

Test 13

Verdict: ACCEPTED

Test 14

Verdict: ACCEPTED

Test 15

Verdict: ACCEPTED

Test 16

Verdict: WRONG ANSWER

Test 17

Verdict: WRONG ANSWER

Test 18

Verdict: ACCEPTED

Test 19

Verdict: ACCEPTED

Test 20

Verdict: WRONG ANSWER

Test 21

Verdict: ACCEPTED

Test 22

Verdict: ACCEPTED

Test 23

Verdict: ACCEPTED