18. 4Sum.js

/**
 * @param {number[]} nums
 * @param {number} target
 * @return {number[][]}
 */
var fourSum = function (nums, target) {
    let result = [];
    nums = nums.sort((a, b) => a - b);
    let n = nums.length;
    if (n < 4) return result;
    for (let i = 0; i < n - 3; i++) {
        if (i > 0 && nums[i] === nums[i - 1]) continue;
        for (let j = i + 1; j < n - 2; j++) {
            if (j > i + 1 && nums[j] === nums[j - 1]) continue;
            let left = j + 1, right = n - 1;
            while (left < right) {
                let sum = nums[i] + nums[j] + nums[left] + nums[right];
                if (sum === target) {
                    result.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--;
                } else if (sum < target) {
                    left++;
                } else {
                    right--;
                }
            }
        }
    }
    return result;
};

console.log(fourSum(nums = [1, 0, -1, 0, -2, 2], target = 0));
console.log(fourSum(nums = [2, 2, 2, 2, 2], target = 8));