70. Climbing Stairs

Posted 2022-12-12 Carl_Hugo

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

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

解题思路：
状态转移方程：

dp[i] = dp[i-1] + dp[i-2]

边界：

dp[1] = 1
dp[2] = 2

public class Solution 
    public int climbStairs(int n) 
        if(n==0||n==1||n==2)return n;
        int[] res = new int[n+1];
        res[0] = 0;
        res[1] = 1;
        res[2] = 2;
        for(int i=3;i<=n;i++)
            res[i] = res[i-1]+res[i-2];
        
        return res[n];