Containers

Pairs

pair<int,string> p;
p=make_pair(3,"abc");
p={4,"cde"};
cout<<p.first<<p.second<<endl;

Pair Array

pair<int,int> p[3];
p[0]={1,4};

pair<int,string> p[3];
swap(p[0],p[1]);
cin>>p.first;
cin>>p.second;

Vectors

Dynamic Array

• Vector Push
• Vector Pop
• Vector Size
• Vector Reference

vector <int> v;
v.push_back(); //O(1)
v.pop_back();
cout<<v.size(); //O(1)
vector <int> v1(10); //all values will be v1
vector <int> v2(10,3); //all valuse will be 3
vector<int> &v3=v2 //passing reference
vector <int>v2=v1 //O(n) we can use assignment operator here;
vector <string>s;

• Nested Vector

vector<pair<int,int>>v;
v.push_back({1,2});
v.push_back(make_pair(1,2));
vector<vector<int>> nestV;

Iterators

• .begin()
• .end()

it++ this moves to the next Iterator but it+1 moves it to the next Location. It it+1 cannot work in map and sets and locations are not continous.

vector <int>v;
v.push_back(10);
vector <int>:: iterator it=v.begin()
cout<<*it<<endl;
for(it=v.begin();it!=v.end;++it)
{
    cout<<(*it);
}

vector<pair<int,int>> vp;
vector<pair<int,int>>::iterator it1;
cout<<(*it1.first);
cout<<(it1->first);
cout<<(it1->second);

//it1->first == *it1.first

Iterator using C++ 11 | Auto Keyword

• Range Based Loops

vector<int>v;
for(int val:v)
{
    value++;//value is copied not referenced
    cout<<val;
}
for(int &val:v)
{
    value++;//value is referenced
    cout<<val;
}

vector<pair<int,int>>vp;
for(pair<int,int> &val:vp)
{
    cout<<val.first<<" "<<val.second;
}

• Auto Keyword

Auto Keyword can automatically understands the datatype.

auto a=1;
auto b="abc";
auto c=1.0;
vector<pair<int,int>>vp;
for(auto &val:vp)
{
    cout<<val.first<<" "<<val.second;
}

Maps

1. Maps (ordered)(red Black trees)
2. Unordered Maps

Key-value pair is stored.

• .size() - gievs the size of the map.

map<int,string> m;
m[1]="abc"; //O(logn)
m[5]="cde";
m[2]="efg";
m.insert({4,"afg"});
map<int,string>::iterator it;
for(auto &val:m)
{
cout<<val.first<<" "<<val.second;
}
cout<<m.size(); //prints m size.
auto itt=m.find(3);//returns iterator else returns m.end(). O(log n)

m.erase(5);//removes keys and values
m.erase(m.find(3));
m.clear(); //clears everything

Insertion of keys of string is string.size()*log(n)

Unordered Maps

Unorderd Map cannot work on pairs!

Use Hash Tables in this. O(1) is time complexity

Every method is taking O(1) like find(),erase()

unordered_map<int,string> m;

Sets

1. Sets
2. Unordered Sets
3. Multiset

set<string> s;
s.insert("avc"); //log(n)
s.insert("def");
s.insert("ghi");
auto it=s.find("abc")//O(log(n)) returns iterator else returns s.end()
s.erase("avc");//removes the record.

Multiset

multiset<string> s;
s.find(); //returns the iterator of first match.
s.erase('abc');// delete all values abc or else if we pass the iterator then it will delete only one

Stacks

stack<int> a;
a.push(3);
a.push(4);
a.push(5);
a.pop();

Queues

queue<int> q;
q.push(4);
q.push(5);
q.empty();

q.front(); //prints the front value
q.pop();

Sorting

sort(starting address, last address+1); //O(nlog(n))

Follow Intro Sort is used in STL.

Upper Bound and Lower Bound

Arrays or vectors should be sorted.

Lower Bound

If the value is present in array or vector than it returns that value and if not present then it returns the value greater then the input that is present in the array.

Upper Bound

Returns the value more than the input value in the array.

int arr[5];
int *ptr=lower_bound(a,a+n,5);//returns the pointer 
int *ptr1=lower_bound(a,a+n,5);//returns the pointer of element greater than 5.

Minimum and Maximum Element

vector<int> v;
int min=*min_element(v.begin(),v.end());//returns pointer.
int max=*max_element(v.begin(),v.end());//returns pointer.

Accumulate

Sums the array.

vector<int>v;
int sum=accumulate(v.begin(),v.end(),initialSum);//initial sum should be 0 for arrray sum

Count and Find, Reverse

Counts the element count.

vector<int> v;
int ct=count(v.begin(),v.end(),3);
int ele=*find(v.begin(),v.end(),2);//returns iterator
auto ele=find(v.begin(),v.end(),2);//returns iterator

if(ele !=v.end())
{
    cout<<*it;
}


reverse(v.begin(),v.end()); //reverse vector or string

Lambda Function

cout<<[](int x,int y){return x+y;}(2,4);

All of, None Of, Any of

All of

vector<int> v;
cout<<all_of(v.begin(),v.end(),[](int x){return x>0;}); //if all true then true else false
cout<<any_of(v.begin(),v.end(),[](int x){return x>0;}); //if any true then true else false
cout<<none_of(v.begin(),v.end(),[](int x){return x>0;}); //if none are true then true else false