guxuerui

const sum = (a, b) => {
  if (a == 0) return b;
  if (b == 0) return a;
  let newA = a ^ b;
  let newB = (a & b) << 1;
  return sum(newA, newB);
}
const a = 10, b = 5;
console.log(sum(a, b)); // 15

guxuerui

// 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;
//     }