STL containers commonly used functions and

C ++ Standard Template Library (Standard Template Library, referred to as STL) is a class library containers and algorithms, commonly used containers with a stack, queue, priorty_queue, set, vector, pair, string and the like, commonly used algorithms sort, max , min, abs, swap, reverse, etc.

All containers support methods

method	description	Examples	time complexity
size	Returns the number of elements of the container	s.size()	O (1)
empty	Determining whether the container is empty, the container is empty, return true	s.empty()	O (1)

Stack (stack)

It included in the stack header file

Features: You can only put in the top of the stack elements, remove elements in the stack, LIFO

method	description	Examples	time complexity
push	Stack (stack)	s.push(x)	O (1)
pop	The stack (stack)	s.pop()	O (1)
top	Returns the top element	s.top()	O (1)

Circular queue (Queue)

It included in the queue header file

Features: You can only remove elements from the team heads into the elements from the tail, FIFO

method	description	Examples	time complexity
push	The team (the tail)	que.push (x)	O (1)
pop	A team (team head)	que.pop ()	O (1)
front	Return the head elements	que.front ()	O (1)
back	Return the tail element	que.back ()	O (1)

Priority queue (The priority_queue)

It included in the queue header file

priority_queue large root can be understood as a binary heap that the top element is the maximum

Declare a value extracted in descending priority queue

priority_queue<int> que;//大根堆

A statement taken from small to large values ​​of the priority queue

priority_queue<int, vector<int>, greater<int> > que;//小根堆

method	description	Examples	time complexity
push	The stack is inserted into the element x	que.push (x)	O (logn)
pop	Delete the top of the heap element	que.pop ()	O (logn)
top	Return to top of the heap element	que.top()	O (1)

Ordered set (set)

Included in the set header file

realized by a red-black tree set, the set of elements is not repeated, the function of automatic deduplication

method	description	Examples	time complexity
clear	Clear	s.clear()	O (n)
insert	Insert elements x	s.insert(x)	O (logn)
find	Returns an iterator elements equal to x. Elements equal to x if not, returns s.end ()	s.find(x)	O (logn)
erase	Delete iterator it points to the elements	s.erase(it)	O (logn)
erase	Delete the equal elements of x	s.erase(x)	O (logn)
count	The returned collection is equal to the number of elements x	s.count(x)	O (logn)

Vector (vector)

Included in the vector header file

vector is a dynamic array, you can use like an array subscript to access elements

method	description	Examples	time complexity
clear	Clear	v.clear()	O (n)
push_back	The element x into the vector tail	v.push_back(x)	O (1)
pop_back	Removes the last element vector tail	v.pop_back	O (1)

Dictionary (map)

It included in the map header file

map is associated with a container, to provide one key value (key-value) mapping

method	description	Examples	time complexity
clear	Clear	m.clear()	O (n)
insert	Insert key-value pairs	m.insert(make_pair(key, value))	O (logn)
find	Find key for the tuple x and returns its iterator	m.find(x)	O (logn)
[] Operator	Return value key is mapped to	m[key]	O (logn)
[] Operator	For m [key] to assignment	m[key] = value	O (logn)

Of the group (pair)

Utility included in the header file, but in general, iostream it also contains

method	description	Examples	time complexity
make_pair	Construct a pair group	make_pair(1, 2)
first	Returns the first element	p.first	O (1)
second	Returns the second element	p.second	O (1)

String (string)

Included in the string header file

string is a class, regardless of memory allocation problem, and provides a range of operational functions

operating	string	char*
definition	string s	char s[105]
Get the first i characters	s[i]	s[i]
Returns the length	s.size()	strlen(s)
Reads one line	getline (eating, s)	gets(s)
Assignment	s = “hello”	strcpy(s, “hello”)
splice	s += “world”	strcat(s, “world”)
Compare	s == “hello”	strcmp(s, “hello”)

The sort function

It included in the algorithm header file

usage: $sort (start address, end address, sorted)$

注意：

1. sort排序的范围是前闭后开，例如：sort(arr, arr+10); 排序的范围是从arr[0]到arr[9]

2. sort的排序方法不写的话，默认是从小到大

从大到小的排序方法

bool cmp(int a, int b)
{	
	return a > b;
}

max、min函数

max(x, y)：返回x和y中的最大值

min(x, y)：返回x和y中的最小值

abs函数

abs(x)：返回x的绝对值，x为整数。

如果要返回浮点数的绝对值，要用math.h头文件下的fabs

swap函数

swap(x, y)：交换x和y的值

reverse函数

reverse(a, b)：可以将数组指针在[a, b)之间的元素或容器的迭代器在[a, b)范围内的元素进行反转。

翻转数组

reverse(arr, arr + n);

翻转string

reverse(s.begin(), s.end());