509. 斐波那契数 70. 爬楼梯 746. 使用最小花费爬楼梯

509. 斐波那契数

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

70. 爬楼梯

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

746. 使用最小花费爬楼梯

class Solution {
    public int minCostClimbingStairs(int[] cost) {
        int a = cost[0];
        int b = cost[1];
        int c = 0;
        for(int i = 2;i < cost.length;i++){
            c = Math.min(a,b) + cost[i];
            a = b;
            b = c;
        }
        return Math.min(a,b);
    }
}