算法|斐波那契数、爬楼梯、使用最小花费爬楼梯

一、 509. 斐波那契数

题目链接：https://leetcode.cn/problems/fibonacci-number/

class Solution {
    public int fib(int n) {
        if (n <= 1) return n;
        int[] dp = new int[n + 1];
        dp[0] = 0;
        dp[1] = 1;
        for (int i = 2; i <= n; i++) {
            dp[i] = dp[i - 1] + dp[i -2];
        }
        return dp[n];
    }
}

class Solution {
    public int fib(int n) {
        if (n <= 1) return n;
        int a = 0;
        int b = 1;
        int c = 0;
        for (int i = 2; i <= n; i++) {
            c = a + b;
            a = b;
            b = c;
        }

        return c;
    }
}

二、 70. 爬楼梯

题目链接：https://leetcode.cn/problems/climbing-stairs/

class Solution {
    public int climbStairs(int n) {
        if (n <= 1) return n;
        int[] dp = new int[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];
    }
}

三、746. 使用最小花费爬楼梯

题目链接：https://leetcode.cn/problems/min-cost-climbing-stairs/

class Solution {
    public int minCostClimbingStairs(int[] cost) {
        int len = cost.length;
        int[] dp = new int[len + 1];
        dp[0] = 0;
        dp[1] = 0;
        for (int i = 2; i < len + 1; i++) {
            dp[i] = Math.min(dp[i - 1] + cost[i - 1], dp[i - 2] + cost[i - 2]);
        }
        return dp[len];
    }
}