function twoSum(nums, target) {
    const prevMap = new Map();
    for (let i=0; i<nums.length; i++) {
        let diff = target - nums[i];
        if (prevMap.has(diff)) {
            return [prevMap.get(diff), i];
        }
        prevMap.set(nums[i], i);
    }
    return [];
}

const nums = [1,2,3,4,5];
console.log(nums);
for (let i=1; i<10; i++) {
    console.log(i, twoSum(nums, i));
}