70. 爬楼梯

一、Java

class Solution {
    public int climbStairs(int n) {  // f(1)=1, f(2)=2, f(3)=3, f(4)=5, f(0)=1
        int pre = 1, cur = 1;
        for (int i = 2; i <= n; i++) {
            cur += pre;
            pre = cur - pre;
        }
        return cur;
    }
}

二、C++

class Solution {
public:
    int climbStairs(int n) {
        int pre = 1, cur = 1;
        for (int i = 2; i <= n; i++) {
            cur += pre;
            pre = cur - pre;
        }
        return cur;
    }
};

三、Python

class Solution:
    def climbStairs(self, n: int) -> int:
        pre, cur = 1, 1
        for i in range(2, n+1):
            cur, pre = cur + pre, cur
        return cur

四、JavaScript

var climbStairs = function (n) {
    let pre = 1, cur = 1;
    for (let i = 2; i <= n; i++) {
        cur += pre;
        pre = cur - pre;
    }
    return cur;
} 

五、Go

func climbStairs(n int) int {
    pre, cur := 1, 1
    for i := 2; i <= n; i++ {
        pre, cur = cur, pre + cur
    }
    return cur
}