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));

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