509. Fibonacci Number
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
Rust Solution
struct Solution;
impl Solution {
fn fib(n: i32) -> i32 {
let mut a: Vec<i32> = vec![0; 31];
a[1] = 1;
for i in 2..=30 {
a[i] = a[i - 1] + a[i - 2];
}
a[n as usize]
}
}
#[test]
fn test() {
assert_eq!(Solution::fib(2), 1);
assert_eq!(Solution::fib(3), 2);
assert_eq!(Solution::fib(4), 3);
}
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