LeetCode 70. Climbing Stairs

Posted 2021-01-16 flowingfog

分析

难度 易

来源

https://leetcode.com/problems/climbing-stairs/

题目

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

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

Note: Given n will be a positive integer.

Example 1:

Input: 2

Output: 2

Explanation: There are two ways to climb to the top.

1. 1 step + 1 step

2. 2 steps

Example 2:

Input: 3

Output: 3

Explanation: There are three ways to climb to the top.

1. 1 step + 1 step + 1 step

2. 1 step + 2 steps

3. 2 steps + 1 step

解答

Runtime: 2 ms, faster than 100.00% of Java online submissions for Climbing Stairs.

 1 package LeetCode;
 2 
 3 public class L70_ClimbingStairs {
 4     //n个台阶的楼梯的走法等于：
 5     //ways(n) = ways(n-1) + ways(n-2)
 6     public int climbStairs(int n) {
 7         int pre1=0,pre2=1,ways=0;//两步前的走法数、一步前的走法数
 8         if(n<=0){
 9             return n;
10         }
11         for(int i=1;i<=n;i++)
12         {
13             ways=pre1+pre2;
14             pre1=pre2;
15             pre2=ways;
16         }
17         return ways;
18     }
19 }