斐波那契数列

• 递归解法

function fibonacci(n){
  if(n === 1 || n === 2) return 1
  return fibonacci(n - 1) + fibonacci(n - 2)
}

• 动态规划解法1

function fibonacci(n) {
  let res = [1, 1]
  for(let i = 2; i < n; i++) {
    res[i] = res[i - 1] + res[i - 2]
  }
  return res[n - 1]
}

• 动态规划解法2

function fibonacci(n){
  let [pre, cur] = [1, 1]
  for(let i = 2; i < n; i++) {
     [pre, cur] = [cur, pre + cur]
  }
  return cur
}