leetcode 70. Climbing Stairs （DP）

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

• 动态规划

C++

class Solution {
public:int climbStairs(int n) {if(n<=2)return n;int f=1,g=2;for(int i=2;i<n;i++){int tmp=g;g=f+g;f=tmp;}return g;}
};

Java

class Solution {public int climbStairs(int n) {if(n<=2)return n;int f=1;int g=2;for(int i=2;i<n;i++){int tmp=g;g=f+g;f=tmp;}return g;}
}

Python

class Solution:def climbStairs(self, n: int) -> int:if n<=2:return nf,g=1,2for i in range(2,n):f,g=g,f+greturn g

Go

func climbStairs(n int) int {if n<=2 {return n}f,g:=1,2for i:=2;i<n;i++ {f,g=g,f+g}return g
}