迭代 时间复杂度 O(n) 空间复杂度 O(1)

/*** @param {number} n* @return {number}*/
var climbStairs = function(n) {let  l = 0, r = 0 , sum = 1for(let i=1; i<=n; ++i){l = rr = sumsum = l + r}return sum
};

 动态规划 时间复杂度 O(n) 空间复杂度 O(n)

/*** @param {number} n* @return {number}*/
var climbStairs = function(n) {if(n==1){return 1}let dp = []dp[1] = 1dp[2] = 2for(let i=3; i<=n; i++){dp[i] = dp[i-1] + dp[i-2]}return dp[n]
};