509. 斐波那契数

题目

链接

代码

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

        return b;
    }
}

70. 爬楼梯

题目

链接

代码

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

746. 使用最小花费爬楼梯

题目

链接

代码

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