https://leetcode-cn.com/problems/qing-wa-tiao-tai-jie-wen-ti-lcof/
- 动态规划
class Solution {
public int numWays(int n) {
if(n==0)return 1;
if(n==1)return 1;
if(n==2)return 2;
int[] arr = new int[n+1];
arr[0]=1;
arr[1]=1;
arr[2]=2;
for(int i=3;i<=n;i++){
arr[i]=arr[i-1]+arr[i-2];
arr[i] %= 1000000007;
}
return arr[n];
}
}
//O(1)空间法
class Solution {
public int numWays(int n) {
int a = 1, b = 1, sum;
for(int i = 0; i < n; i++){
sum = (a + b) % 1000000007;
a = b;
b = sum;
}
return a;
}
}
