singleNumber , ex: [4,1,2,1,2]

var singleNumber = function(nums) {

    var ans = 0;

    for (var i = 0; i < nums.length; i++) {

        ans = ans ^ nums[i];

    }

    return ans;

};

example1:

Input: nums = [4,1,2,1,2]

Output: 4

containsDuplicate 利用arr-key取代第二個for-loop

 var containsDuplicate = function(nums) {

    const arr=[]

     for(let i=0;i<nums.length;i++) {

        

        if(arr[nums[i]]) {

            return true

        }else {

            arr[nums[i]]= true

         }  

    }

    return false

};

Example 1:

Input: nums = [1,2,3,1]

Output: true

Example 2:

Input: nums = [1,2,3,4]

Output: false

時間字符串被格式化為hh:mm:ss並基於 24 小時制，字符串比較的默認行為就足夠了

 https://bobbyhadz.com/blog/javascript-compare-two-time-strings

const time1 = '07:30:24';
const time2 = '10:45:33';

if (time1 > time2) {
  console.log('time1 is greater than time2');
} else if (time2 > time1) {
  // ✅ this runs
  console.log('time2 is greater than time1');
} else {
  console.log('time1 is equal to time2');
}

why-is-my-css3-transition-delaying-before-it-starts

 https://stackoverflow.com/questions/30627250/why-is-my-css3-transition-delaying-before-it-starts

可試試這個文章 https://css-tricks.com/using-css-transitions-auto-dimensions/ 看能不能解