Fibonacci.js

// let n = parseInt(process.argv[2]); // convert string to int

// let first = 0;
// let second = 1;

// let s = first + " " + second;

// if (n === 0) {
//     console.log([]);
//     return;
// }

// if (n == 1){
//     console.log(s.substring(0,1));
//     return;
// }

// //       first  second  nextNum
// // 3 =>  0      1       1

// let nextNum = first + second; // 1

// for (let i = 3; i <= n; i++) {
//     s = s + " " + nextNum;
//     first = second;
//     second = nextNum;
//     nextNum = first + second;
// }

// if (n >= 2) {
//     console.log(s);
// }


// 0 => []
// 1 => [0]
// 2 => [0 , 1] sequence = 
// 3 => [0 1 1]
// 4 => [0 1 1 2]

// let s = "0 1";
// let first = 0;
// let second = 1;
// let nextNum;

// let n = parseInt(process.argv[2]);

// if(n <=0){
//     console.log("Enter a positive number.");
// }else if(n === 1 ){
//     console.log(s.substring(0 ,1));
// } else {
//     console.log(fibonacci(n-2));
// }

// function fibonacci(n){
//     if(n > 0){
//         nextNum = first +second;
//         s = s + " "+nextNum;
//         first = second;
//         second = nextNum;
//         fibonacci(n-1);
//     }
//     return s;
// }

let F = []; // it is used to store values which is return by the fib function
// THis is the concept of memoziation which increases the performance of function.
// It is used to avoid excessive recursion;
// Excessive recursion is a function which is called multiple times for the same parameter.


// function fib(n){
//     if(n<=1){
//         F[n] = n;
//         return n;
//     }
//     return fib(n-2) + fib(n-1);    
// }

function fib(n){
    if(n<=1){
        F[n] = n;
        return n;
    }else{
        if(!F[n-2]){
            F[n-2] = fib(n-2);
        }
        if(!F[n-1]){
            F[n-1] = fib(n-1);
        }
        return F[n-2] + F[n-1];
    }    
}

console.log(fib(parseInt(process.argv[2])));