Groupon_interview-fib-numbers.js

// write function for fibonacci numbers where
// F[1]=F[2]=1; F[3]=2; F[4]=3; => 1,1,2,3,5,8,...
const fibRec = n => {
  if (n === 1 || n === 2) {
    return 1
  }
  return fibRec(n-1) + fibRec(n-2)
}

const fibImp = n => {
  let previous = 1
  let prePrevious = 1
  let result = 1
  
  if (n < 3) {
    return result
  }
  
  for(let i = 2; i < n; i++) {
    result = prePrevious + previous
    
    prePrevious = previous
    previous = result
  }
  
  return result
}

// TEST
console.log(fibImp(1) === 1)
console.log(fibImp(2) === 1)
console.log(fibImp(4) === 3)
console.log(fibImp(100000) === fibImp(99999) + fibImp(99998))