991. 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. 1 <= X <= 10^9
  2. 1 <= Y <= 10^9

Rust Solution

struct Solution;

impl Solution {
    fn broken_calc(x: i32, mut y: i32) -> i32 {
        let mut res = 0;
        while y > x {
            if y % 2 == 0 {
                y /= 2;
            } else {
                y += 1;
            }
            res += 1;
        }
        res + x - y
    }
}

#[test]
fn test() {
    let x = 2;
    let y = 3;
    let res = 2;
    assert_eq!(Solution::broken_calc(x, y), res);
    let x = 5;
    let y = 8;
    let res = 2;
    assert_eq!(Solution::broken_calc(x, y), res);
    let x = 3;
    let y = 10;
    let res = 3;
    assert_eq!(Solution::broken_calc(x, y), res);
    let x = 1024;
    let y = 1;
    let res = 1023;
    assert_eq!(Solution::broken_calc(x, y), res);
}

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