斐波那契数列
    1，1，2，3，5，8…..
    fib(n) = fib(n-1) + fib(n-2);
    实现

    1. // 普通递归
    2. function originfib (n) {
    3.   console.log(n);
    4.   if (n === 1 || n === 2) {
    5.     return 1;
    6.   }
    7.   return originfib(n - 1) + originfib(n - 2);
    8. }
    9. // 改进递归 v1 v2存值，
    10. function fibonacci (n) {
    11.   function fib (n, v1, v2) {
    12.     console.log(n, v1, v2);
    13.     if (n === 1) {
    14.       return v1;
    15.     } else if (n === 2) {
    16.       return v2;
    17.     } else {
    18.       return fib(n - 1, v2, v1 + v2);
    19.     }
    20.   }
    21.   return fib(n, 1, 1);
    22. }
    23. // 循环
    24. function fibFor (n) {
    25.   var n1 = 1, n2 = 1, sum = 1;
    26.   for (let i = 2; i < n; i++) {
    27.     sum = n1 + n2;
    28.     n1 = n2;
    29.     n2 = sum;
    30.     console.log(sum);
    31.   }
    32.   return sum;
    33. }
    34. // 循环 + 解构赋值
    35. function newFibFor (n) {
    36.   var n1 = 1, n2 = 1;
    37.   for (let i = 2; i < n; i++) {
    38.     [n1, n2] = [n2, n1 + n2];
    39.   }
    40.   return n2;
    41. }

    https://www.cnblogs.com/superlizhao/p/11603158.html
    https://blog.csdn.net/weixin_43738731/article/details/84256666