Leetcode OJ 70 Climbing Stairs [Easy]

Leetcode OJ 70. Climbing Stairs

题目描述：

You are climbing astair case. It takes n steps to reach to the top.

Each time you caneither climb 1 or 2 steps. In how many distinct ways can you climb to the top?

Note: Given n will be a positive integer.

题目理解：

爬n阶楼梯，每次只能爬1阶或2阶，求有多少种不同的方式爬到顶端

测试用例：

功能测试：奇数、偶数、边界1

分析：

1.  爬1阶有1种方式

2.  爬2阶有2种方式

3.  爬3阶= 爬1阶的方式+爬2阶的方式，即爬3阶相当于从1阶爬上来或从2阶爬上来

4.  爬n阶= 爬n-2阶的方式+爬n-1阶的方式

解答：

public static int climbStairs(int n){    int stepprepre= 1;    int steppre= 2;    int ans = 0;    if(n == 1)return 1;    if(n == 2)return 2;    for(int i = 3; i <= n; i++){        ans = stepprepre + steppre;       stepprepre = steppre;        steppre = ans;    }    return ans;}

简洁的解答：

public int climbStairs(int n) {    int a = 1, b = 1;    while (n-- > 0)        a = (b += a) - a;    return a;}