斐波那契数列（1,1,2,3,5,8,13,21,34,55,89...求第 n 项）

斐波那契数列（1,1,2,3,5,8,13,21,34,55,89…求第 n 项）

• 递归
  普通版

function feibonaqishu1 (n){
  if (n<=1) {return 1}
  return feibonaqishu1(n-1)+feibonaqishu1(n-2)
}

优化版

function feibonaqishu2 (n , ac1 = 1 , ac2 = 1) {
  if( n <= 1 ) {return ac2};
  return feibonaqishu2(n - 1, ac2, ac1 + ac2);
}

• 循环版

function feibonaqishu3 (n) {
   if( n === 1 || n===2 ) {return 1};
   let ac1 = 1, ac2 = 1;
   for (let i = 2; i < n; i++) {
     [ac1, ac2] = [ac2, ac1 + ac2];
   }	  
   return ac2
}