Priyanshu Tiwari

STL Cheat Sheet

Posted on Dec 25, 2020

pair

  • utility container
  • Used to store two data object in a single container
#include <iostream>
using namespace std

int main(){
  pair<int, int> p1;
  pair<int, int> p2(303, 52);
  pair<int, char> p3(1, 'a');
  pair<int, int> p4(p3);
  pair<int, int> p5 = {2, 'b'};
  pair<int, int> p6 = make_pair('A', 1);
}

Input/Output

cout << p.first << " " << p.second;

vector

  • Linear data structure
  • Contigous in memory
  • Dynamic in size
  • Random access
  • Fast traversal
  • Insertion and deletion at rear node

Initialization

#include <vector>
using namespace std;

int main(){

  vector<int> v1;
  vector<int> v2 {1,2,3};
  vector<int> v3(v2);
  vector<int> v4 = v3;
  vector<int> v5(10);
  vector<int> v6(10, -1);

}

Input/Output

for(int i=0; i<n; i++)
  cin >> v[i];

for(int i=0; i<n; i++)
  cout << v[i] << " ";

for(int i=0; i<n; i++){
  cin << ele;
  v.push_back(ele);
}

for(auto e: v)
  cout << e << " ";

Access/Insertion/Deletion


// Returns size of the vector
v.size();

// Returns true if vector is empty
v.empty();

// unsafe : Segmentation Fault
v[i];

// safe : Out-Of-Bound Exception
v.at(i);

int f = v.front();
int b = v.back();

// inserts at the beginning
v.insert(v.begin(), x);


// inserts at the ending
v.push_back(ele);
v.emplace_back(ele);

// removes the last element
v.pop_back();

// removes the first element
v.erase(v.begin());

// removes the last element
v.erase(v.end())

//flushes the vector
v.clear();

Sorting

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

reverse(v.begin(), v.end(), greater<int>());

Max/Min

int* maxi =  *max_element(v.begin(), v.end());
int* mini =  *min_element(v.begin(), v.end());
cout << *mini << " " << *maxi << endl;

Upper/Lower Bound

  • Upper : Just greater then x
  • Lower : Not less than x
vector<int>::iterator lower, upper;
lower = lower_bound(v.begin(), v.end(), 42);
upper = upper_bound(v.begin(), v.end(), 42);
cout << (lower - v.begin() + 1) << " " << (upper - v.begin() + 1);

2D vector

// Intialization
vector<vector<int>> v1( n , vector<int> (m));
vector<vector<int>> v2( n , vector<int> (m, -1));

for(int i = 0; i < n; i++){
    for(int j = 0; j < m; j++)
        cout << v[i][j] << " ";
    cout << "\n";
}

for(vector<int> v: v1){
    for(int i: v)
        cout << i << " ";
    cout << "\n";
}

// Sorting a single row
sort(vec[i].begin(), vec[i].end());


// Sorting the whole vector
bool comp(const vector<int>& v1, const vector<int>& v2){
    return v1[1] < v2[1];
}

sort(vec.begin(), vec.end(), comp);
v.size()Returns the size current size
v.max_size()Returns the size maximum possible size
v.empty()Returns true if vector is empty
v[i]Accessing $i_{th}$ element (unsafe: Can cause segmentation errors)
v.at()Accessing $i_{th}$ element (safe: throws exception when out-of-bound)
v.front()Accessing the first element
v.back()Accessing the last element
v.push_back(data)Inserts at the end
v.emplace_back(data)Inserts at the end but bit more efficiently
v.insert(pos_itr, data)Inserts at specified position
v.fill(data)Fill the whole vector with ‘data’
for (auto e : v)Looping through the vector

array

  • Linear data structure
  • Contigous in memory
  • Fixed in size
  • Random access
  • Fast traversal
#include <array>
using namespace std;

int main(){

  array<int> a;
  array<int, 3> b{1,2,3};
  array<int> c = b;

}
a.size()Returns the size current size
a.max_size()Returns the size maximum possible size
a.empty()Returns true if array is empty
a[i]Accessing $i_{th}$ element (unsafe: Can cause segmentation errors)
a.at()Accessing $i_{th}$ element (safe: throws exception when out-of-bound)
a.front()Accessing the first element
a.back()Accessing the last element
a.fill(data)Fill the whole array with ‘data’
for (auto e : a)Looping through the array

list

  • Doubly Linked List

string

queue

  • Linear data structure.

deque

Map

  • Implemented via balanced binary tree.

unordered_map

  • Implemented via hash table

set

  • Implemented via balanced binary tree.

unordered_set

  • Implemented via hash table

Algorithms