O2优化

#### 输入输出格式

• Line 1: Two space-separated integers: N and M.

• Lines 2..M+1: Each line contains two space-separated integers representing two lights that are connected. No pair will be repeated.

• Line 1: A single integer representing the minimum number of switches that need to be flipped in order to turn on all the lights.

5 6
1 2
1 3
4 2
3 4
2 5
5 3


3

#### 分析及解决

• 折半搜索 < meet in the middle >

2018.04.12

• 正解：高斯消元

• TeX parse error: Undefined control sequence \[

（保证每盏灯最后都是亮的）

• TeX parse error: Undefined control sequence \[

......

• TeX parse error: Undefined control sequence \[

2018.04.21

#### AC代码

折半搜索 meet in the middle unordered_map 最慢点 Time:28ms / Memory:8250KB -O2 map 最慢点 Time:44ms / Memory:9746KB -O2