两数之和

给定 nums = [2, 7, 11, 15], target = 9

因为 nums[0] + nums[1] = 2 + 7 = 9
所以返回 [0, 1]

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

    return []
};