algorithm: nth Fibonacci Number

Maths/Fibonacci.ts

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+/**
+ * A function to get nth Fibonacci number
+ * @param number The input integer
+ * @return {number} Fibonacci number of `number`
+ * @example nthFibonacci(4) => 3 | nthFibonacci(6) => 8
+ * @see https://en.m.wikipedia.org/wiki/Fibonacci_number
+ * @author MohdFaisalBidda <https://github.com/MohdFaisalBidda>
+ */
+
+export const nthFibonacci = (number: number): number => {
+  if (number < 0)  throw "Number should be greater than 0";
+
+  if (number === 0)  return 0;
+
+  let a = 0, b = 1;
+
+  for (let i = 1; i < number; ++i) {
+    const c = a + b;
+
+    a = b;
+    b = c;
+  }
+
+  return b;
+};

Maths/test/Fibonacci.test.ts

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+import {nthFibonacci} from '../Fibonacci';
+
+describe('nthFibonacci', () => {
+  test('should return correct value', () => {        
+    expect(nthFibonacci(0)).toBe(0);  
+    expect(nthFibonacci(1)).toBe(1);
+    expect(nthFibonacci(5)).toBe(5);
+    expect(nthFibonacci(4)).toBe(3);
+    expect(nthFibonacci(0)).toBe(0);
+  });
+});