JS简单基础算法

斐波那契数列

 function fib(n){
    let num=0
    if(n<=2){
     return num=1
    }
  return  num=fib(n-1)+fib(n-2)
  }

斐波那契数列求和

function fibSum(n) {
    let num = 0,
      a = 1,
      b = 1,
      sum = 0;
      if (n <= 2) {
        return sum = n === 1 ? 1 : 2
      }   
      for(let i=3;i<=n;i++){
        num=a+b;
        a=b;
        b=num
        sum+=num
      }
      return sum+2
    }

阶乘

function jc(n){
  let num=1
    for(let i=1;i<=n;i++){
      num*=i
    }
    return num
  }

阶乘求和

 function jc(n) {
    let num = 1,
      sum = 0
    for (let m = 0; m < n; m++) {
      for (let i = 1; i <= n; i++) {
        num *= i
        sum += num
      }
      return sum
    }
  }