leetcode 70. climb stairs

difficulty ： Simple
The frequency of ：88
subject ：
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 ？

** Their thinking ：** Dynamic equation -

• It has nothing to do with the process , It's only about the result
• Dynamic programming is used for Multistage decision making problem ;（ The relationship between the current stage and the previous stage ===》 State transition equation ）
• The question of dynamic programming ： Just ask the optimal solution , Don't ask for specific solutions ;
  Code ：

class Solution {
    
    public int climbStairs(int n) {
    
        // Because there is f[n], That is, the length is n+1
        int f[]=new int[n+1];  // State definition ====f[n] It is defined as to n Step by step method to plant trees 
        f[0]=1;  // There is only one way to stay still 
        f[1]=1;  // There is only one way to get to the first step 
        //  According to the state transfer equation ,i Only from 2 Start , Don't cross the border 
        for(int i=2;i<=n;i++){
    
            // State transition equation 
            f[i]=f[i-1]+f[i-2];
        }
        return f[n];
    }
}