跳台阶

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题目描述

一只青蛙一次可以跳上1级台阶，也可以跳上2级。求该青蛙跳上一个n级的台阶总共有多少种跳法（先后次序不同算不同的结果）。

解题思路

f(n) = f(n-1) + f(n-2)

代码实现

递归

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class Solution {
public:
    int jumpFloor(int number) {
        if (number < 1){
            return 0;
        } else if (number == 1) {
            return 1;
        } else if (number ==2) {
            return 2;
        } else {
            return jumpFloor(number - 1) + jumpFloor(number - 2);
        }
    }
};

非递归

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class Solution {
public:
    int jumpFloor(int number) {
        if (number < 1){
            return 0;
        }
        
        if ((number == 1) || (number == 2)){
            return number;
        }
        
        int first = 2, second = 1, sum = 0;
        
        for (int i = 3; i <= number; i++) {
            sum = first + second;
            second = first;
            first = sum;
        }
        return sum;
    }
};