斐波那契数列中从 1 到 N 的数字之和

给定一个整数N ，任务是找出斐波那契数列中从1到N的数字之和。
前几个斐波那契数是1, 1, 2, 3, 5, 8, 13, 21, 34, ....
例子：

Input: N = 5
Output: 12
1 + 1 + 2 + 3 + 5 = 12
Input: N = 10
Output: 20
1 + 1 + 2 + 3 + 5 + 8 = 20

方法：

循环遍历所有小于N的斐波那契数。
用0初始化sum变量。
继续添加这些斐波那契数以获得所需的总和。

下面是上述方法的实现：

C++

// C++ implementation of the approach
#include 
using namespace std;
 
// Function to return the
// required sum
int fibonacciSum(int N)
{
 
    if (N == 0)
        return 0;
 
    // Generate all Fibonacci numbers <= N
    // and calculate the sum
    int sum = 0;
    int a = 1, b = 1, c;
    sum += a;
    while (b <= N) {
 
        sum += b;
        int c = a + b;
        a = b;
        b = c;
    }
    return sum;
}
 
// Driver code
int main()
{
    int N = 20;
    cout << fibonacciSum(N);
 
    return 0;
}

Java

// Java implementation of the approach
class GFG
{
     
// Function to return the
// required sum
static int fibonacciSum(int N)
{
 
    if (N == 0)
        return 0;
 
    // Generate all Fibonacci numbers <= N
    // and calculate the sum
    int sum = 0;
    int a = 1, b = 1, c;
    sum += a;
    while (b <= N)
    {
 
        sum += b;
        c = a + b;
        a = b;
        b = c;
    }
    return sum;
}
 
// Driver code
public static void main(String[] args)
{
    int N = 20;
    System.out.println(fibonacciSum(N));
}
}
 
// This code is contributed by Code_Mech.

Python3

# Python3 implementation of
# the approach
 
# Function to return the
# required sum
def fibonacciSum(N):
 
    if N == 0:
        return 0
 
    # Generate all Fibonacci
    # numbers <= N and calculate
    # the sum
    Sum = 0
    a, b = 1, 1
    Sum += a
    while b <= N:
 
        Sum += b
        a, b = b, a + b
     
    return Sum
 
# Driver code
if __name__ == "__main__":
 
    N = 20
    print(fibonacciSum(N))
 
# This code is contributed
# by Rituraj Jain

C#

// C# implementation of the approach
using System;
 
class GFG
{
     
// Function to return the
// required sum
static int fibonacciSum(int N)
{
 
    if (N == 0)
        return 0;
 
    // Generate all Fibonacci numbers <= N
    // and calculate the sum
    int sum = 0;
    int a = 1, b = 1, c;
    sum += a;
    while (b <= N)
    {
 
        sum += b;
        c = a + b;
        a = b;
        b = c;
    }
    return sum;
}
 
// Driver code
public static void Main()
{
    int N = 20;
    Console.WriteLine(fibonacciSum(N));
}
}
 
// This code is contributed by Code_Mech.

PHP

Javascript

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