两数之和

/**
 * @param {number[]} nums
 * @param {number} target
 * @return {number[]}
 */
var twoSum = function(nums, target) {
    let  map = new Map()
    for(let i=0,l=nums.length;i<l;i++){
        if(map.get(nums[i]) !== undefined){
            return [map.get(nums[i]),i]
        }else{
            map.set(target-nums[i],i)
        }
    }
    return []
}