991. Broken Calculator
摘要：
On a broken calculator that has a number showing on its display, we can perform two operations:
Double: Multiply the number on the display b...
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
難度：medium
題目：在一個顯示數字的壞計算器上，我們可以執行兩個操作:
加倍:將顯示的數字乘以2，或; 遞減:從顯示的數字中減去1。 最初，計算器顯示的是數字X。 返回顯示數字Y所需的最小運算元。
思路：從Ｙ到Ｘ，可執行的操作為自增1和減半。如果為奇數則自增1,如果為偶則減半。如果Ｘ大於Ｙ則只能自減。
Runtime: 3 ms, faster than 100.00% of Java online submissions for Broken Calculator.
Memory Usage: 36.6 MB, less than 100.00% of Java online submissions for Broken Calculator.
class Solution {
public int brokenCalc(int X, int Y) {
int step = 0;
while (X != Y) {
if (Y < X) {
step += X - Y;
break;
}
Y = Y % 2 == 1 ? Y + 1 : Y / 2;
step++;
}
return step;
}
}