菲波那切数列

fib.js

// const fib  = (num) => {
//   if (num <= 0) return 0;
//   if (num === 1 || num === 2) return 1;
//   if (num > 2) {
//     let prev = 1, next = 1;
//     for (let i = 3; i <= num; i++) {
//       let sum = prev + next;
//       prev = next;
//       next = sum;
//     }
//     return next;
//   }
// };
let map = {
  0: 0,
  1: 1
};
const fib  = (num) => {
  if (map[num] === undefined) map[num] = fib(num - 1) + fib(num - 2);
  return map[num];
};

fib = n => {
  if (typeof n !== "number") {
     throw new Error("..");
   }
  if (n < 2) {
     return n;
   }
  let a = 0;
  let b = 1;
  while (n--) {
    [a, b] = [b, a + b];
  }
  return a;
};

膜拜大佬👏