【leetcode】两数之和，hashmap解题，空间换时间

/**
 * @param {number[]} nums
 * @param {number} target
 * @return {number[]}
 */
var twoSum = function(nums, target) {
    const prevNum={};
    for(let i=0;i<nums.length;i++){
        const curNum=nums[i];
        const targetNum=target-curNum;
        const targetNumIndex=prevNum[targetNum];
        if(targetNumIndex!==undefined){
            return [targetNumIndex,i];
        }else{
            prevNum[curNum]=i;
        }
    }
};