Common methods of vector containers

vector

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1. 初始化：
   $vector<int>s$
   is the definition of not allocating space in advance. At this time, the output value of s.size() is 0. At this time,
   we cannot access the elements in s through the index of s. We can only use the s.push_back(x) function or s .insert(posion, x) to automatically expand the capacity. After expansion, we can access the elements inside through the subscript.
   $vector<int>s\left(100\right)$
   This is the way of allocating memory in advance, so that s is given 100 int memory in advance, and thenwe output the value of s.size() will be 100, and i can access 0 to 99 through the index Values ​​between, but the values ​​are all 0, and can also be assigned and initialized by adding a parameter after 100, which is the initial value of the hundred elements

2. You can save the number
   by s.push_back(x), insert an element at the end
   s.insert(posion, x) insert x before the iterator posion, note that the first parameter here is an iterator, similar to s.begin()
   Store the value s[1] = 3 through the array subscript;

3. Delete
   s.erase(posion) Delete the number of the iterator at posion position
   s.pop_back() is to delete the last value

4. Query
   To query a value, you can directly use the index to query
   or use the method to query the value of a specific position.
   s.front() is the first value
   s.back() is the last value

5. Commonly used functions are lower_bound(), sort().
   For lower_bound, you can check my solution
   link
   about lower_bound . Return an iterator that is not less than x in s.
   lower_bound(s.begin(), s.end(), x ); sort
   the elements in s
   sort(s.begin(), s.end(), cmp);
   cmp is a custom sorting function implementation method:
   bool cmp(int x, int y)
   { return x > y ;Sort in descending order (customizable) } If you don't write the second parameter, it will be in ascending order by default