The Fibonacci numbers, commonly denoted F(n) form a sequence, called the Fibonacci sequence, such that each number is the sum of the two preceding ones, starting from 0 and 1. That is,
F(0) = 0, F(1) = 1 F(N) = F(N - 1) + F(N - 2), for N > 1.
Given N, calculate F(N).
Example 1:
Input: 2 Output: 1 Explanation: F(2) = F(1) + F(0) = 1 + 0 = 1.
Example 2:
Input: 3 Output: 2 Explanation: F(3) = F(2) + F(1) = 1 + 1 = 2.
Example 3:
Input: 4 Output: 3 Explanation: F(4) = F(3) + F(2) = 2 + 1 = 3.
Note:
0 ≤ N ≤ 30.
Related Topics:
Array
Similar Questions:
- Climbing Stairs (Easy)
- Split Array into Fibonacci Sequence (Medium)
- Length of Longest Fibonacci Subsequence (Medium)
// OJ: https://leetcode.com/problems/fibonacci-number/
// Author: github.com/lzl124631x
// Time: O(N)
// Space: O(1)
class Solution {
public:
int fib(int N) {
if (!N) return 0;
if (N == 1) return 1;
int prev = 0, cur = 1;
while (--N > 0) {
int tmp = prev + cur;
prev = cur;
cur = tmp;
}
return cur;
}
};