Climbing Stairs

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?

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

Constraints:

  • 1 <= n <= 45

Solution:

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

发布者

常轩

常轩

总要做点什么吧!

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