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