70. 爬楼梯

//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

/*
Date: 2019/11/25
Author: xzping
function: leetcode70 Climb Stairs
*/

package main

import "fmt"

func ClimbStairs(n int) int {
    if n == 1 {
        return 1
    }
    if n == 2 {
        return 2
    }
    return ClimbStairs(n-1) + ClimbStairs(n-2)
}

func ClimbStairs2(n int) int {
    if n == 1 {
        return 1
    }
    if n == 2 {
        return 2
    }
    var sta, sta1, sta2 int = 0, 1, 2
    for i := 3; i <= n; i++ {
        sta = sta1 + sta2
        sta1 = sta2
        sta2 = sta
    }
    return sta

}

func main() {
    var n int
    n = ClimbStairs(9)
    fmt.Println("n = ", n)
    n = ClimbStairs2(9)
    fmt.Println("n = ", n)
}