代码随想录35期Day38-Java(Day37休息)

Day38题目

LeetCode509.斐波那契数列

核心思想:很简单dp[i]=dp[i-1]+dp[i-2].这里用了数组存储的形式,也可以递归

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

LeetCode70.爬楼梯

核心思想:和斐波那契一样

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

LeetCode746.最小花费爬楼梯

核心思想:每次选择从i-1和i-2中最小花费的爬就行.

class Solution {
    public int minCostClimbingStairs(int[] cost) {
        int[] dp = new int[cost.length+1];
        dp[0] = cost[0];
        dp[1] = cost[1];
        for(int i = 2 ; i < cost.length ; i ++){
            dp[i] = Math.min(dp[i-1] ,dp[i-2]) + cost[i]; 
        }
        // 返回顶层-1 和 顶层-2的最小值
        return Math.min(dp[cost.length-2],dp[cost.length-1]);
    }
}