### Problem

Given an array S of n integers, are there elements a, b, c, and d in S such that a + b + c + d = target? Find all unique quadruplets in the array which gives the sum of target.

Note:
Elements in a quadruplet (a,b,c,d) must be in non-descending order. (ie, a ≤ b ≤ c ≤ d)
The solution set must not contain duplicate quadruplets.

### Example

given array S = {1 0 -1 0 -2 2}, and target = 0.
A solution set is:
(-1,  0, 0, 1)
(-2, -1, 1, 2)
(-2,  0, 0, 2)

### JavaScript Code

```function fourSum(num, target) {
num.sort();

var hashSet = [];
var result = [];

for (var i = 0; i < num.length; i++) {
for (var j = i + 1; j < num.length; j++) {
var k = j + 1;
var l = num.length - 1;

while (k < l) {
var sum = num[i] + num[j] + num[k] + num[l];

if (sum > target) {
l--;
} else if (sum < target) {
k++;
} else if (sum == target) {
var temp = [];
temp.push(num[i]);
temp.push(num[j]);
temp.push(num[k]);
temp.push(num[l]);

if (hashSet[temp] == null) {
hashSet.push(temp);
result.push(temp);
}

k++;
l--;
}
}
}
}

return result;
}

console.log(fourSum([1,0,-1,0,-2,2], 1));
```