LeetCode 70. Climbing Stairs

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.

package LeetCode;

public class L70_ClimbingStairs {
    //n个台阶的楼梯的走法等于：
    //ways(n) = ways(n-1) + ways(n-2)
    public int climbStairs(int n) {
        int pre1=0,pre2=1,ways=0;//两步前的走法数、一步前的走法数
        if(n<=0){
            return n;
        }
        for(int i=1;i<=n;i++)
        {
            ways=pre1+pre2;
            pre1=pre2;
            pre2=ways;
        }
        return ways;
    }
}