366. Fibonacci【Naive】

Find the Nth number in Fibonacci sequence.

A Fibonacci sequence is defined as follow:

• The first two numbers are 0 and 1.
• The i th number is the sum of i-1 th number and i-2 th number.

The first ten numbers in Fibonacci sequence is:

0, 1, 1, 2, 3, 5, 8, 13, 21, 34 ...

Notice

The Nth fibonacci number won't exceed the max value of signed 32-bit integer in the test cases.

 

Example

Given 1, return 0

Given 2, return 1

Given 10, return 34

题意

查找斐波纳契数列中第 N 个数。

所谓的斐波纳契数列是指：

• 前2个数是 0 和 1 。
• 第 i 个数是第 i-1 个数和第i-2 个数的和。

解法一：

 class Solution {
 public:
     /*
      * @param n: an integer
      * @return: an ineger f(n)
      */
     int fibonacci(int n) {
         int a, b;
         a = ;
         b = ;

         for (int i = ; i < n; i++) {
             int c = a + b;
             a = b;
             b = c;
         }
         return a;
     }
 };

解法二：

 class Solution {
 public:
     /*
      * @param n: an integer
      * @return: an ineger f(n)
      */
     int fibonacci(int n) {
         if (n == ) {
             return ;
         } else if (n == ) {
             return ;
         }

         return fibonacci(n - ) + fibonacci(n - );

     }
 };

递归会超时