Double linked list

List

begin() and end():

An iterator pointing to the starting position of the container is obtained by calling the member function begin() of the list container. The next position at the end of the list can be obtained by calling the end() function of the list container, which is equivalent to the nth + 1st position a[n] in int a[n]. In fact, it does not exist and cannot be accessed. It is often used as a condition for judging the end of the loop.

push_back() and push_front():

Use the member function push of list_ Back and push_front inserts an element into the list. Where push_back() is inserted from the end of the list, while push_ The implementation of front () is inserted from the head of the list.

empty():

Use empty() to determine whether the list is empty.

front() and back()

pop_back and pop_front()

reverse():

Reverse the list through reverse().

merge():

Merge two linked lists and make them in ascending order by default (you can also change it), l1.merge(l2, greater()); After the call, l2 becomes empty. The elements in l1 contain the elements in l1 and l2, and are arranged in descending order. In addition, greater () can be changed or not arranged in ascending order (for example, in structure arrangement)

bool listsort(int a,int b){
	if(a>b)
		return true;
	return false;
}
int main ()
{
    list<int> IntList;
    list<int> IntList2(3,5);
    for( int i=0; i < 10; i++ )
    	IntList.push_front( i);
    IntList.merge(IntList2, listsort);
    for(iter=IntList.begin();iter!=IntList.end();iter++){
    	cout<<*iter<< " ";
    }
	cout<<endl;
	return 0;
}

insert():

Insert one or more elements at the specified location (three overloads):

l1.insert(l1.begin(),100); stay l1 Insert 100 at the start of the.
l1.insert(l1.begin(),2,200); stay l1 Insert two 100's at the beginning of the.
l1.insert(l1.begin(),l2.begin(),l2.end());stay l1 Insert from l2 Elements at all positions from start to end.

Stack

Stack

Out of stack: push()

Stack pressing: pop()

Whether the stack is empty: empty()

Stack size: size()

Access stack top: top()

queue

code implementation

#include <iostream>
#define elemtype int
#define MAX 10
using namespace std;
struct Queue
{
    elemtype q[MAX];
    int front = 0;
    int rear = 0;
};
//Determine whether the queue is full
bool isfull(Queue Q)
{
    if ((Q.rear + 1) % MAX == Q.front)
    {
        return true;
    }
    else
    {
        return false;
    }
}
// Destroy queue
void destroy(Queue &Q)
{
    delete &Q;
    cout << "DESTROYED" << endl;
}
// Empty queue
void erase(Queue &Q)
{
    Q.front = 0;
    Q.rear = 0;
    cout << "ERASED" << endl;
}

// Get queue header element
elemtype Qhead(Queue Q)
{
    return Q.q[Q.front];
}
// Insert element at end of queue
void Qenter(Queue &Q, elemtype n)
{
    if (isfull(Q))
    {
        cout << "QUENE IS FULL" << endl;
    }
    else
    {
        Q.q[Q.rear] = n;
        Q.rear = (Q.rear + 1) % MAX;
        cout << "ENTERED" << endl;
    }
}
// Delete queue header element
elemtype Qdelete(Queue &Q)
{
    if (Qlenth(Q) == 0)
    {
        cout << "QUENE IS EMPTY" << endl;
        return -1;
    }
    else
    {
        int result = Q.front;
        Q.front = (Q.front + 1) % MAX;
        cout << "DELETED" << endl;
        return Q.q[result];
    }
}

Queue

back() returns the last element

empty() returns true if the queue is empty

front() returns the first element

pop() deletes the first element

push() adds an element at the end

size() returns the number of elements in the queue

sort

sort()

The template of the sort function has three parameters:

void sort (RandomAccessIterator first, RandomAccessIterator last, Compare comp);

(1) The first parameter, first, is the starting address of the array to be sorted.

(2) The second parameter, last: is the end address (the address of the last data after the last data)

(3) The third parameter comp is the sorting method: it can be in ascending or descending order. If the third parameter is not written, the default sorting method is to sort from small to large.

struct node
{
    int data;
};
bool cmp(node a, node b)
{
    return a.data > b.data;//From big to small
}

Tree and binary tree

Binary tree

//BinaryTree
struct Tree
{
    char data;
    Tree *lchild;
    Tree *rchild;
};
//Preorder traversal binary tree
void PreOrder(Tree *T)
{
    if (T != NULL)
    {
        cout << T->data << ' ';
        PreOrder(T->lchild);
        PreOrder(T->rchild);
    }
}
//Traversing binary tree by layer
void LevelOrder(Tree *T)
{
    queue<Tree *> Q;
    Q.push(T);
    while (!Q.empty())
    {
        Tree *t = Q.front();
        Q.pop();
        cout << t->data << ' ';
        if (t->lchild != NULL)
        {
            Q.push(t->lchild);
        }
        if (t->rchild != NULL)
        {
            Q.push(t->rchild);
        }
    }
}
//Duplicate binary tree
Tree* Tcopy(Tree *T)
{
    if (T == NULL)
    {
        return NULL;
    }
    else
    {
        Tree *copy = new Tree;
        copy->data = T->data;
        copy->lchild=Tcopy(T->lchild);
        copy->rchild=Tcopy(T->rchild);
        return copy;
    }
}
//Count nodes
int Tcount_node(Tree*T)
{
    if(T==NULL)
    {
        return 0;
    }
    else
    {
        return Tcount_node(T->lchild) + Tcount_node(T->rchild) + 1;
    }
}
//Count the number of leaves
int Tcount_leaf(Tree*T)
{
    if(T==NULL)
    {
        return 0;
    }
    if(T->lchild==NULL&&T->rchild==NULL)
    {
        return 1;
    }
    else
    {
        return Tcount_leaf(T->lchild) + Tcount_leaf(T->rchild);
    }
}

Hash table

The < operator is overloaded with map for the structure, and unordered for the structure_ Map overload = = operator

unordered_map

unordered_map The iterator of is a pointer to this element and obtains its value through the iterator.

1 unordered_map<Key,T>::iterator it;
2 (*it).first;             // the key value (of type Key)
3 (*it).second;            // the mapped value (of type T)
4 (*it);                   // the "element value" (of type pair<const Key,T>) 
Its key values are iterators first and second Properties. 

1 it->first;               // same as (*it).first   (the key value)
2 it->second;              // same as (*it).second  (the mapped value) 
Member function:
=================iterator ========================= 
begin 　　Returns an iterator that points to the beginning of the container( iterator) 
end 　　   Returns an iterator pointing to the end of the container 
cbegin　   Returns a constant iterator that points to the beginning of the container( const_iterator) 
cend 　　 Returns a constant iterator pointing to the end of the container 
=================Capacity================ 
size  　　 Returns the number of valid elements 
max_size  return unordered_map Maximum number of elements supported 
empty        Judge whether it is empty 
=================Element access================= 
operator[]  　　   Access element 
at  　　 　　　　Access element 
=================Element modification================= 
insert  　　Insert element 
erase　　   Delete element 
swap 　　   Exchange content 
clear　　   Empty content 

int main()  
{  
	//Note: C++11 only supports bracket initialization
    unordered_map<int, string> myMap={{ 5, "Zhang Da" },{ 6, "Li Wu" }};//Assignment with {}
    myMap[2] = "Li Si";  //Use [] for single insertion. If the key value 2 already exists, the assignment will be modified. If not, it will be inserted.
    myMap.insert(pair<int, string>(3, "Chen er"));//Insert using insert and pair
  
	//Use of traversal output + iterator
    auto iter = myMap.begin();//auto automatically recognizes as iterator type unordered_map < int, string >:: iterator
    while (iter!= myMap.end())
    {  
        cout << iter->first << "," << iter->second << endl;  
        ++iter;  
    }  
	
	//Find elements and output the use of + iterators
    auto iterator = myMap.find(2);//find() returns an iterator pointing to 2
    if (iterator != myMap.end())
	    cout << endl<< iterator->first << "," << iterator->second << endl;  
    system("pause");  
    return 0;  
}  

map

begin() returns an iterator that points to the map header

clear() deletes all elements

count() returns the number of occurrences of the specified element

empty() returns true if the map is empty

end() returns the iterator that points to the end of the map

erase() deletes an element

find() finds an element

lower_bound() returns the key value > = the first position of the given element

rbegin() returns an inverse iterator that points to the tail of the map

rend() returns an inverse iterator that points to the map header

size() returns the number of elements in the map

upper_bound() returns the key value > the first position of a given element

To determine whether a data (keyword) is displayed in the map

The first method is to use the count function to determine whether the keyword appears. The disadvantage is that it is unable to locate the location where the data appears. Due to the characteristics of map and the one-to-one mapping relationship, the return value of the count function is only two, either 0 or 1. In case of occurrence, of course, 1 is returned

The second is to use the find function to locate the location where the data appears. It returns an iterator. When the data appears, it returns the iterator where the data is located. If there is no data to be found in the map, the iterator it returns is equal to the iterator returned by the end function.

Priority queue

In the priority queue, the elements with higher priority go out of the queue first.
The standard library uses the < operator of element types by defau lt to determine the priority relationship between them.

priority_queue<int>q;

Output elements from small to large

At this point, we can pass in a comparison function

priority_queue<int, vector<int>, greater<int> >q;

Custom priority

Compare priorities in elements by customizing the operator < operator

struct node
{
    friend bool operator< (node n1, node n2)
    {
        return n1.priority < n2.priority;
    }
    int priority;
    int value;
};

In this structure, value is the value and priority is the priority.

Joint search set

initialization

int fa[MAXN];
inline void init(int n)
{
    for (int i = 1; i <= n; ++i)
        fa[i] = i;
}

query

int find(int x)
{
    if(fa[x] == x)
        return x;
    else
        return find(fa[x]);
}

Merge (path compression)

int find(int x)
{
    if(x == fa[x])
        return x;
    else{
        fa[x] = find(fa[x]);  //Set parent node as root node
        return fa[x];         //Return parent node
    }
}

chart

dijkstra algorithm (shortest path)

#include <bits/stdc++.h>
#define INF 1000000
using namespace std;
int flag[1010];
int dis[1010];
int graph[1010][1010];
int n;
void dijkstra()
{
    memset(flag, 0, sizeof(flag));
    for (int i = 1; i <= n; i++)
    {
        dis[i] = INF;
    }
    dis[1]= 0;
    for (int i = 1; i <= n; i++)
    {
        int find, min = INF;
        for (int j = 1; j <= n; j++)
        {
            if (!flag[j] && dis[j] <= min)
            {
                min = dis[j];
                find = j;
            }
        }
        flag[find] = 1;
        for (int j = 1; j <= n; j++)
        {
            if (dis[j] > dis[find] + graph[find][j])
            {
                dis[j] = dis[find] + graph[find][j];
            }
        }
    }
}
int main()
{
    int m;
    cin >> n >> m;
    memset(graph, INF, sizeof(graph));
    for (int i = 0; i < m; i++)
    {
        int x, y, d;
        cin >> x >> y >> d;
        if (d < graph[x][y])
        {
            graph[x][y] = graph[y][x] = d;
        }
    }
    dijkstra();
    if (dis[n] != INF)
    {
        cout << dis[n]<<endl;
    }
    else
    {
        cout << "-1" << endl;
    }
    return 0;
}

prime algorithm (minimum spanning tree)

#include <iostream>
#include <fstream>
using namespace std;

#define MAX 100
#define MAXCOST 0x7fffffff

int graph[MAX][MAX];

int prim(int graph[][MAX], int n)
{
    int lowcost[MAX];
    int mst[MAX];
    int i, j, min, minid, sum = 0;
    for (i = 2; i <= n; i++)
    {
        lowcost[i] = graph[1][i];
        mst[i] = 1;
    }
    mst[1] = 0;
    for (i = 2; i <= n; i++)
    {
        min = MAXCOST;
        minid = 0;
        for (j = 2; j <= n; j++)
        {
            if (lowcost[j] < min && lowcost[j] != 0)
            {
                min = lowcost[j];
                minid = j;
            }
        }
        cout << "V" << mst[minid] << "-V" << minid << "=" << min << endl;
        sum += min;
        lowcost[minid] = 0;
        for (j = 2; j <= n; j++)
        {
            if (graph[minid][j] < lowcost[j])
            {
                lowcost[j] = graph[minid][j];
                mst[j] = minid;
            }
        }
    }
    return sum;
}