karateChop.js

Array.prototype.findHalf = function () {
  return Math.floor(this.length/2);
};

Array.prototype.isEmpty = function () {
  return this.length === 0;
};

Array.prototype.first = function () {
  return this[0];
};

Array.prototype.last = function () {
  return this[this.length-1];
};

//

let recurChop = (target,array,index) => {

  if (array.isEmpty() ||
      array.first() > target ||
      array.last() < target) {return -1;}

  if (array.first() === target) {return index;}

  let newArr = null,
      half = array.findHalf(),
      firstSlice = array.slice(0,half),
      firstLen = firstSlice.length;

  if (firstSlice.last() < target) {
    newArr = array.slice(half);
    index+=firstLen;
    return recurChop(target,newArr,index);
  }
  return recurChop(target,firstSlice,index);
  
};

let chop = (target,array) => {
  return recurChop(target,array,0);
};

//

let chop2 = (target,array) => {

  let index = 0;

  if (array.first() > target ||
      array.last() < target ||
      array.isEmpty()) {
    return -1;
  }

  while (array.first() != target) {
    let half = array.findHalf(),
        firstSlice = array.slice(0,half);

    if (firstSlice.last() < target) {
      array = array.slice(half);
      if (array.length > 1) {
        index += array.length;
      }
    } else {
      array = firstSlice;
    }
  }

  return index;

};

//

let chop3 = (target,array) => {

  let index = 0;
  if (array.first() > target ||
        array.last() < target ||
        array.isEmpty()) {
      return -1;
    }

    for (let i = 0; array.first() != target; i++) {
      let half = array.findHalf(), 
          firstSlice = array.slice(0,half);

      if (firstSlice.last() < target) {
        array = array.slice(half);
        if (array.length > 1) {
          index += array.length;
        }
      } else {
        array = firstSlice;
      }

    }
    return index;
};


module.exports = {
  chop,
  chop2,
  chop3
};