solution.js

/**
 * @param {number[]} nums
 * @param {number} target
 * @return {number[][]}
 */
var fourSum = function (nums, target) {
    const result = [];
    nums.sort((a, b) => a - b);
    let index1 = 0;
    while (index1 < nums.length - 3) {
        // index1固定 转化为3Sum了
        let index2 = index1 + 1;
        while (index2 < nums.length - 2) {
            let index3 = index2 + 1;
            let index4 = nums.length - 1;
            while (index3 < index4) {
                const sum = nums[index1] + nums[index2] + nums[index3] + nums[index4];
                if (sum > target) {
                    index4--;
                } else if (sum < target) {
                    index3++;
                } else {
                    result.push([
                        nums[index1], nums[index2], nums[index3], nums[index4],
                    ]);
                    const val3 = nums[index3++];
                    const val4 = nums[index4--];
                    // 跳过重复元素
                    while (index3 < index4 && nums[index3] === val3) {
                        index3++;
                    }
                    while (index3 < index4 && nums[index4] === val4) {
                        index4--;
                    }
                }
            }
            // 跳过重复元素
            const val2 = nums[index2++];
            while (index2 < nums.length - 2 && nums[index2] === val2) {
                index2++;
            }
        }
        // 跳过重复元素
        const val1 = nums[index1++];
        while (index1 < nums.length - 3 && nums[index1] === val1) {
            index1++;
        }
    }
    return result;
};