## 672. Bulb Switcher II

There is a room with `n`

lights which are turned on initially and 4 buttons on the wall. After performing exactly `m`

unknown operations towards buttons, you need to return how many different kinds of status of the `n`

lights could be.

Suppose `n`

lights are labeled as number [1, 2, 3 ..., n], function of these 4 buttons are given below:

- Flip all the lights.
- Flip lights with even numbers.
- Flip lights with odd numbers.
- Flip lights with (3k + 1) numbers, k = 0, 1, 2, ...

**Example 1:**

Input:n = 1, m = 1.Output:2Explanation:Status can be: [on], [off]

**Example 2:**

Input:n = 2, m = 1.Output:3Explanation:Status can be: [on, off], [off, on], [off, off]

**Example 3:**

Input:n = 3, m = 1.Output:4Explanation:Status can be: [off, on, off], [on, off, on], [off, off, off], [off, on, on].

**Note:** `n`

and `m`

both fit in range [0, 1000].

## Rust Solution

```
struct Solution;
impl Solution {
fn flip_lights(n: i32, m: i32) -> i32 {
let n = n.min(3);
if m == 0 || n == 0 {
return 1;
}
if n == 1 {
return 2;
}
if n == 2 {
return if m == 1 { 3 } else { 4 };
}
if m == 1 {
return 4;
}
if m == 2 {
7
} else {
8
}
}
}
#[test]
fn test() {
let n = 1;
let m = 1;
let res = 2;
assert_eq!(Solution::flip_lights(n, m), res);
let n = 2;
let m = 1;
let res = 3;
assert_eq!(Solution::flip_lights(n, m), res);
let n = 3;
let m = 1;
let res = 4;
assert_eq!(Solution::flip_lights(n, m), res);
}
```

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