## 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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