C Program to Find the Sum of Fibonacci Numbers at Even Indexes up to N Terms
Here, we will build a C Program to Find the Sum of Fibonacci numbers at even indexes up to N terms
Fibonacci Numbers: 0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, ……
Input:
N = 5
Output:
88 // Sum of the elements at even indexes = 0 + 1 + 3 + 8 + 21 + 55 = 88
Approach:
This approach includes solving the problem directly by finding all Fibonacci numbers till 2n and adding up only the even indices numbers from the array.
Example:
C
// C Program to find the sum of // even-indices Fibonacci numbers #include <stdio.h> // Computes value of the first // fibonacci numbers and stores // the even-indexed sum int calculateEvenSum( int n) { // return 0 if n is equals or less than to 0 if (n <= 0) return 0; int fibo[2 * n + 1]; fibo[0] = 0, fibo[1] = 1; // Initialize the result int sum = 0; // Adding the remaining terms for ( int i = 2; i <= 2 * n; i++) { fibo[i] = fibo[i - 1] + fibo[i - 2]; // For even indices if (i % 2 == 0) sum += fibo[i]; } // Return alternating sum return sum; } // Driver Code int main() { // Get n int n = 5; // calculateEvenSum(n) function is computed and return // the sum of even-indices Fibonacci numbers. int sum = calculateEvenSum(n); // display result printf ( "Even indexed Fibonacci Sum upto %d terms = %d" , n, sum); return 0; } |
Output
Even indexed Fibonacci Sum upto 5 terms = 88
Time Complexity: O(N)
Space Complexity: O(1)