509

Author: ProHiryu

Math/509.md

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+## 509 Fibonacci Number
+
+#### Description
+
+[link](https://leetcode.com/problems/fibonacci-number/)
+
+---
+
+#### Solution
+
+- See Code
+
+---
+
+#### Code
+
+<!-- O(n) -->
+
+```python
+class Solution:
+    def fib(self, N: int) -> int:
+        if N == 0:
+            return 0
+        if N == 1:
+            return 1
+        x_0 = 0
+        x_1 = 1
+        for i in range(2, N + 1):
+            x_2 = x_0 + x_1
+            x_0 = x_1
+            x_1 = x_2
+        return x_2
+```