70. 爬楼梯

题目如下：

https://leetcode.cn/problems/climbing-stairs/description/?envType=study-plan-v2&envId=dynamic-programming

思路：动态规划。关键是找到递推关系，写出动态规划的转移方程。

Java代码如下：

`import java.util.Scanner;

public class Solution {
public static void main(String[] args) {
Scanner scanner=new Scanner(System.in);
System.out.println(climbStairs(scanner.nextInt()));
}
public static int climbStairs(int n){
if (n<4){
return n;
}
int a=1,b=2,c=3;
for (int i = 4; i <= n; i++) {
a=b;
b=c;
c=a+b;
}
return c;
}
}
`