21. Broken Calculator.cpp

/*
Broken Calculator
=================

On a broken calculator that has a number showing on its display, we can perform two operations:

Double: Multiply the number on the display by 2, or;
Decrement: Subtract 1 from the number on the display.
Initially, the calculator is displaying the number X.

Return the minimum number of operations needed to display the number Y.

Example 1:
Input: X = 2, Y = 3
Output: 2
Explanation: Use double operation and then decrement operation {2 -> 4 -> 3}.

Example 2:
Input: X = 5, Y = 8
Output: 2
Explanation: Use decrement and then double {5 -> 4 -> 8}.

Example 3:
Input: X = 3, Y = 10
Output: 3
Explanation:  Use double, decrement and double {3 -> 6 -> 5 -> 10}.

Example 4:
Input: X = 1024, Y = 1
Output: 1023
Explanation: Use decrement operations 1023 times.

Note:
1 <= X <= 10^9
1 <= Y <= 10^9
*/

class Solution
{
public:
  int brokenCalc(int x, int y)
  {
    int count = 0;
    while (y != x)
    {
      if (x >= y)
        return ((x - y) + count);
      if (y % 2 == 0)
        y = y / 2;
      else
        y++;
      count++;
    }
    return count;
  }
};