509. Fibonacci Number

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509. Fibonacci Number

Description

Difficulty: Easy

Related Topics: Math, Dynamic Programming, Recursion, Memoization

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,

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F(0) = 0, F(1) = 1
F(n) = F(n - 1) + F(n - 2), for n > 1.

Given n, calculate F(n).

Example 1:

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Input: n = 2
Output: 1
Explanation: F(2) = F(1) + F(0) = 1 + 0 = 1.

Example 2:

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Input: n = 3
Output: 2
Explanation: F(3) = F(2) + F(1) = 1 + 1 = 2.

Example 3:

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Input: n = 4
Output: 3
Explanation: F(4) = F(3) + F(2) = 2 + 1 = 3.

Constraints:

  • 0 <= n <= 30

Hints/Notes

  • simplest dp

Solution

Language: C++

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class Solution {
public:
    int fib(int n) {
        if (n == 0 || n == 1) {
            return n;
        }
        vector<int> nums{0, 1};
        for (int i = 2; i <= n; i++) {
            nums.push_back(nums[i - 1] + nums[i - 2]);
        }
        return nums[n];
    }
};