1. 注意命名的时候不要重复
2. 注意边界条件

3. 联系一下类的书写和继承

4. vector 去除重复元素：

    vector<vector<int>> myvec;
   
    sort\(myvec.begin\(\),myvec.end\(\)\);
   
    myvec.erase\(unique\(myvec.begin\(\),myvec.end\(\)\),myvec.end\(\)\);
   

5. static bool compare(const Interval& a, const Interval& b){

   return a.start < b.start;
   

   }

   sort(intervals.begin(),intervals.end(),compare);

6. permutation

1. power of n

https://leetcode.com/problems/power-of-three/discuss/77876/**-A-summary-of-all-solutions-(new-method-included-at-15:30pm-Jan-8th\)