18. 4Sum.js

/**
 * @param {number[]} nums
 * @param {number} target
 * @return {number[][]}
 */
var fourSum = function(nums, target) {
    nums = nums.sort((a, b) => a - b);
    const quadruplets = [];
    for(let i=0;i<nums.length-3;i++){
        if(i>0 && nums[i] === nums[i-1]) continue;
        for(let j=i+1;j<nums.length-2;j++){
            if(j>i+1 && nums[j] === nums[j-1]) continue;
            let left = j+1;
            let right = nums.length-1;
            while(left<right){
                const sum = BigInt(nums[i])+BigInt(nums[j])+BigInt(nums[left])+BigInt(nums[right]);
                if(sum<target){
                    left++;
                }else if(sum>target){
                    right--;
                }else{
                    quadruplets.push([nums[i], nums[j], nums[left], nums[right]]);
                    while(left<right && nums[left] === nums[left+1]){
                        left++;
                    } 
                    while(left<right && nums[right] === nums[right-1]){
                        right--;
                    }
                    left++;
                    right--;
                }   
            }
        }
    }
    return quadruplets;
};

var nums = [2,2,2,2,2];
const target = 8;
console.log(fourSum(nums, target));