4sum.js

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