[Problem Solving] pageCount

문제 이해 :

• Arguments
  (1) n : total number of pages in the book
  (2) p : page of interest
• Conditions
  (1) end goal is to reach the page of interest
  (2) must begin flipping pages on either the first page or the last page of the book
  (3) must flip one page at a time to reach the page of interest
  (4) the book is read from left to right direction (5) page 1 will always begin on the right side
  (6) last page can either be on left or right side depending on the total number of pages in the book
• Return
  (1) return the minimum number of page flips required to reach the page of interest

해결 방법 :

• Decide where to begin (front or back) If the page of interest is greater than half of total number of pages, start from the last page. Else, start from the first page. Then,
• Create a for loop that increments/decrements page number by 2 everytime the loop is run. This loop should stop and return the number of flips if current page is equal or greater/less than the page of interest.
  If the book is read from the front, current page should equal or be greater than the page of interest. However, if flipping starts from the back, current page should equal or be less than the page of interest.

  코드 구현 :

    function pageCount(pagesTotal, page) {
  if (page <= pagesTotal / 2) {
    var currentPage = 1;
  
    for (var flips = 0; currentPage < pagesTotal; flips++) {
    if (currentPage >= page) return flips;
    currentPage += 2;
    }
  } else {
    var currentPage = pagesTotal;
  
    for (var flips = 0; currentPage > pagesTotal / 2; flips++) {
    if (currentPage <= page) return flips;
    currentPage -= 2;
    }
  }
    }
  

결과 분석 :

• test case 1 failed “expected 1 to deeply equal 0”
  • There was an extra flip in the loop when started from the back of the book when the page
• test case 2 failed “expected 71 to deeply equal 70”
  • same problem occurred as above

해결 방법 :

• Account for odd number of total pages so that there is no extra flip to reach the page of interest.
  • If the total number of pages is an odd number, subtract one from it and set it as the current page.
  • If the total number of pages is an even number, set it as the current page.

코드 구현 :

  function pageCount(pagesTotal, page) {
    if (page <= pagesTotal / 2) {
      var currentPage = 1;

      for (var flips = 0; currentPage < pagesTotal; flips++) {
      if (currentPage >= page) return flips;
      currentPage += 2;
      }
    } else {
      var currentPage = pagesTotal % 2 === 0 ? pagesTotal : pagesTotal - 1;

      for (var flips = 0; currentPage > pagesTotal / 2; flips++) {
      if (currentPage <= page) return flips;
      currentPage -= 2;
      }
    }
  }

결과 분석 :

• All tests passed !