Two Sum

function twoSum(nums, target) {
    let result = [],
        cache = {};
    for (let i = 0; i < nums.length; i++) {
        let x = target - nums[i];
        if (cache[x] !== undefined) {
            result.push([cache[x], i]);
        }
        cache[nums[i]] = i;
    }

    return result;
};