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07_fibonacci.cpp
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07_fibonacci.cpp
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/*
* Copyright(c) 2019 Jiau Zhang
* For more information see <https://github.com/JiauZhang/algorithms>
*
* This repo is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation
*
* It is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with THIS repo. If not, see <http://www.gnu.org/licenses/>.
*/
/*
* 题目描述:
* 大家都知道斐波那契数列,现在要求输入一个整数n,
* 请你输出斐波那契数列的第n项(从0开始,第0项为0)。
*
*/
/* 递归方法----效率低,内存占用大 */
class Solution {
public:
int Fibonacci(int n) {
if (n <= 0)
return 0;
if (n == 1)
return 1;
return Fibonacci(n-1) + Fibonacci(n-2);
}
};
/* 循环方法----效率高,避免了递归中的重复计算 */
class Solution {
public:
int Fibonacci(int n) {
if (n <= 0)
return 0;
if (n == 1)
return 1;
int f_n_1 = 1;
int f_n_2 = 0;
int f_n = 0;
for (int i=2; i<=n; i++) {
f_n = f_n_1 + f_n_2;
f_n_2 = f_n_1;
f_n_1 = f_n;
}
return f_n;
}
};