February 13, 2022-2-climbing stairs

Suppose you're climbing the stairs . need n You can reach the top of the building .

Every time you climb 1 or 2 A stair . How many different ways can you climb to the top of the building ？

Example 1：

Input ：n = 2
Output ：2
explain ： There are two ways to climb to the top .

1. 1 rank + 1 rank
2. 2 rank
   Example 2：

Input ：n = 3
Output ：3
explain ： There are three ways to climb to the top .

1. 1 rank + 1 rank + 1 rank
2. 1 rank + 2 rank
3. 2 rank + 1 rank

Tips ：

1 <= n <= 45

java Code ：

class Solution {
    public int climbStairs(int n) {
        if(n ==1 || n ==2) {
            return n;
        }

		// Dynamic programming 
        int[] dp = new int[n+1];
        dp[0] =1;
        dp[1] = 1;

        for(int i=2;i<=n;i++) {
            dp[i] = dp[i-1] + dp[i-2];
        }

        return dp[n];
    }
}