70. Climbing Stairs

难度: Easy

题目描述

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

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

 

Example 1:

Input: n = 2
Output: 2
Explanation: There are two ways to climb to the top.
1. 1 step + 1 step
2. 2 steps

Example 2:

Input: n = 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

 

Constraints:

• 1 <= n <= 45

解题思路

代码实现

解决方案

java

class Solution {
    public int climbStairs(int n) {

        int anc = 1;
        int pre = 1;

        for (int i = 2; i <= n; i++) {
            int cur = anc + pre;
            anc = pre;
            pre = cur;
        }
        return pre;

    }
}