2019-05-10 F2E workshop Day4

Day4 討論內容:

• 費氏數列遞迴&迭代解
• setTimeout面試題
• 頁面渲染過程

/**
509. Fibonacci Number
Easy

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The Fibonacci numbers, commonly denoted F(n) form a sequence,
called the Fibonacci sequence,
such that each number is the sum of the two preceding ones,
starting from 0 and 1. That is,

F(0) = 0,   F(1) = 1
F(N) = F(N - 1) + F(N - 2), for N > 1.
Given N, calculate F(N).

 
///////地回
function fibonacci(n){
if(n<1){return 0}
else if(n<=2){return 1}
else {return fibonacci(n-1)+fibonacci(n-2) }
}




Example 1:

Input: 2
Output: 1
Explanation: F(2) = F(1) + F(0) = 1 + 0 = 1.
Example 2:

Input: 3
Output: 2
Explanation: F(3) = F(2) + F(1) = 1 + 1 = 2.
Example 3:

Input: 4
Output: 3
Explanation: F(4) = F(3) + F(2) = 2 + 1 = 3.
 

Note:

0 ≤ N ≤ 30.


 * @param {number} N
 * @return {number}
 */
Example: [0 1 1 2 3 5 ...]
var fib = function(N) {
    //recursive
  if(N<1){
    return 0;
  }else if(N<=2){
    return 1;
  }else {
    return fib(N-1)+fib(N-2);
  }
};


var fib = function(N) {
  //loop
  var temp = [0,1,1];
  for(var i = 3; i <= N; i++) {
    // F(N) = F(N - 1) + F(N - 2)
    temp.push(temp[i-1] + temp[i-2]);
  }
  return temp[N];
  
  if(N<2){
    return N;
  }
  var curr,prev=1,0;
  for(i=2;i<n;i++){
    [curr,prev]=[curr+prev,curr];
  }
  return curr;
  
};
var fib = (function() {
  //Optimize recursion with memory function  
  var memo = {};
  function f(n) {
    var value;
    
    if (n in memo) {
      value = memo[n];
    } else {
      if (n === 0 || n === 1)
        value = n;
      else
        value = f(n - 1) + f(n - 2);

      memo[n] = value;
    }
    
    return value;
  }
  
  return f;
})();


//Timeout
以下程式碼會列印出什麼？
for (var i = 1; i <= 5; i++) {
  setTimeout( function timer() {
      console.log(i);
  }, i * 1000 );
}
this.
this.

~~~~
for (var i = 1; i <= 5; i++) {
    setTimeout(function(i) {
      console.log(i);
    }, i * 1000,i);
  }
~~~~
  
文碩:6 6 6 6 6
昀生:6 6 6 6 6
Tyson:6 6 6 6 6


//Timeout part2
console.log(1);
setTimeout(()=>{
    console.log(3)
},0);
console.log(2);
文碩:1 2 3
昀生: 123~
Tyson:1 2 3

1. Ajax是什麽? 如何創建一個Ajax？ 
2. 頁面渲染過程。
3. 前端優化