70. Climbing Stairs

public class Solution {
    public int climbStairs(int n) {
        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];
    }
}

递归：时间复杂度2^n

public class Main {
    public static void climbstair(Stack stack,int n){
        if(n>=1){
            stack.push(1);
            climbstair(stack,n-1);
            stack.pop();
        }
        if(n>=2){
            stack.push(2);
            climbstair(stack,n-2);
            stack.pop();
        }
        if(n==0){
            for(int i:stack){
                System.out.println("step"+i+"->");
            }
            System.out.println("finish");
        }
    }
    
    public static void main(String[] args) {
        Stack stack=new Stack<>();
        climbstair(stack,5);
    }
}