70. 爬楼梯

Posted 2022-10-11 xuzhaoping

//到达n阶只可能来自n-1和n-2,所以f(n)=f(n-1)+f(n-2)
//1 2 3 5 8 13
int climbStairs(int n)
    if (n == 1)
        return 1;
    if (n == 2)
        return 2;
    int sta = 0, sta1 = 1, sta2 = 2;
    for (int i = 3; i <= n; i++) 
        sta = sta1 + sta2;
        sta1 = sta2;
        sta2 = sta;
    
    return sta;

class Solution:
    def climbStairs(self, n: int) -> int:
        if n == 1: 
            return 1
        
        if n == 2: 
            return 2
        
        stat1, stat2 = 1, 2
        for i in range(3, n+1): 
            sum = stat1 + stat2
            stat1 = stat2
            stat2 = sum
        
        return sum