509. 斐波那契数

class Solution {
public:int fib(int n) {if (n == 0) return 0;if (n == 1) return 1;return fib(n-1) + fib(n-2);}
};

70. 爬楼梯

class Solution {
public://动态规划 -- 爬楼梯int climbStairs(int n) {if (n <= 1) return n; //防止空指针vector<int> dp(n+1);dp[1] = 1;dp[2] = 2;for (int i = 3; i <= n; i++){dp[i] = dp[i-1]+dp[i-2];}return dp[n];}
};

746. 使用最小花费爬楼梯

class Solution {
public:int minCostClimbingStairs(vector<int>& cost) {int n = cost.size();vector<int> dp(n+1, 0);for (int i = 2; i < n+1; i++) {dp[i] = min(dp[i-1] + cost[i-1], dp[i-2] + cost[i-2]);}return dp[n];}
};