### PROBLEM LINK:

**Author:** Misha Chorniy

**Tester:** Tuan Anh Tran Dang

**Translators:** Sergey Kulik (Russian), Team VNOI (Vietnamese) and Hu Zecong (Mandarin)

**Editorialist:** Tuan Anh Tran Dang

## DIFFICULTY

CAKEWALK

## PREREQUISITE

NONE

## PROBLEM

Given 4 distinct numbers check if there is exist a sub-set of numbers with sum equals zero.

# SOLUTION

4 is small enough for us to just consider all possible sub-sets. I think most of the contestant will choose bitmask to implement the solution. Each sub-set can be represented by a 4-bit number where each bit 1 corresponding to a number that is chosen. You can refer to the pseudo code below:

```
result = "No"
for s 1 -> 15:
sum = 0;
for i 0 -> 3
if bit ith of s is 1 then sum += a[i]
if sum = 0:
result = "Yes";
break;
```