Array Challenge Arithmetic / Geometric

arithGeo.ts

function isArithmetic(arr: number[]): boolean {
  return arr.every((x: number, i: number) => {
    if (i < 2) {
      return true;
    }
    
    return arr[i] - arr[i-1] === arr[i-1] - arr[i-2];
  });
}

function isGeometric(arr: number[]): boolean {
  return arr.every((x: number, i: number) => {
    if (i < 2) {
      return true;
    }

    if (arr[i-1] == 0 || arr[i-2] == 0) {
      return false;
    }

    return arr[i] / arr[i-1] === arr[i-1] / arr[i-2];
  });
}


function arithGeo(arr: number[]): string | -1 {
  if (isArithmetic(arr)) {
    return 'Arithmetic';
  } 
  
  if (isGeometric(arr)) {
    return 'Geometric';
  }
  
  return -1;
}


console.log(arithGeo([5, 10, 15]));
console.log(arithGeo([1,2,4,8]));
console.log(arithGeo([-5, 0, 5]));
console.log(arithGeo([-5, 0, 3]));
console.log(arithGeo([1,2,4,6,8,10]));