LC 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:

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

 

Example 1:

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

 

Example 2:

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

 

Example 3:

Input: n = 3, m = 1.
Output: 4
Explanation: 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].

Runtime: 4 ms, faster than 29.00% of C++ online submissions for Bulb Switcher II.

找规律题。

class Solution {
public:
    int flipLights(int n, int m) {
      if(m == 0) return 1;
      if(n == 1) return 2;
      if(n == 2 && m == 1) return 3;
      if(n == 2) return 4;
      if(m==1) return 4;
      if(m == 2) return 7;
      return 8;
    }
};