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: n = 2 Output: 1 Explanation: F(2) = F(1) + F(0) = 1 + 0 = 1.
Example 2:
Input: n = 3 Output: 2 Explanation: F(3) = F(2) + F(1) = 1 + 1 = 2.
Example 3:
Input: n = 4 Output: 3 Explanation: F(4) = F(3) + F(2) = 2 + 1 = 3.
Constraints:
0 <= n <= 30
Related Topics:
Math, Dynamic Programming, Recursion, Memoization
Similar Questions:
- Climbing Stairs (Easy)
- Split Array into Fibonacci Sequence (Medium)
- Length of Longest Fibonacci Subsequence (Medium)
- N-th Tribonacci Number (Easy)
// 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 <= 1) return n;
int a = 0, b = 1;
while (--n > 0) {
a += b;
swap(a, b);
}
return b;
}
};