C++ Data Structures Cheat Sheet by Hackin7

//Append ::iterator to your data type declaration to create an iterator of
that data type
vector<int>::iterator it; // declares an iterator of vector<int>

// loops from the start to end of vi
for(vector<int>::iterator it = vi.begin(); it != vi.end(); it++) 
    cout << *it << " "; // outputs 1 2 3 4

deque<int> d;
deque<int>::iterator it;
it = d.begin(); //Points to first element 
it++; // Points to next element
it = d.end(); // Points to Last element
it--; // Points to previous element
cout << *it; // outputs the element it is pointing

map<string, int> M;
M[“hello”] = 2;
M[“asd”] = 986;

M.count(“asd”); // returns 1
M.count(“doesnt_exist”); // returns 0
M.size(); 

// Check for the existence of some key in the map - O(log N)
it = M.find(“asd”); //returns the iterator to “asd”
it = M.upper_bound("aaa");
it = M.lower_bound("aaa");
if (it == M.end())
    cout << "Does not exist\n";

//Iteration
for (auto it = mp.begin(); it != mp.end(); ++it) {
    cout << it.first << “, “ << it.second << “\n”;
}

queue<int> q;

q.push(5); // Inserts/ Enqueue element at the back of the queue

q.front(); // Returns element atb the front of the queue
q.pop // Removes (Dequeues) element from the front of the queue

q.empty(); // Returns boolean value of whether queue is empty

priority_queue<data_type> pq; // Largest at top
priority_queue<data_type, vector<data_type>, greater<data_type> >
pq; // Smallest at top

pq.push(5); // pushes element into it. Duplicates are allowed
pq.top() // Returns largest or smallest element
pq.pop() // Removes largest or smallest element

pq.size(); // Returns size
pq.empty(); Check if queue is empty

//Below here can mix & match
long long ft[100001]; // note: this fenwick tree is 1-indexed.
////PUPQ//////////////////////////////////////////////////////
void fenwick_update(int pos, long long value) {
    while (pos <= N) {
        //cout<<"Fenwick Updating: "<<pos<<","<<value<<endl;
        ft[pos] += value;
        
        pos += pos&-pos;
    }
}
long long fenwick_query(int pos) {
    long long sum = 0;
    while (pos) { // while p > 0
        sum += ft[pos];
        pos -= pos&-pos;
    }
    return sum;
}
////RUPQ//////////////////////////////////////////////////////
void fenwick_range_update(int pos_a, int pos_b, int val){
    //TLE way
    //for (int i=pos_a;i<=pos_b;i++){fenwick_update(i, val);}
    fenwick_update(pos_a, val);
    fenwick_update(pos_b+1, -val);
}
////PURQ////////////// ////////////////////////////////////////
long long fenwick_range_query(int pos_a, int pos_b) {
    return fenwick_query(pos_b) - fenwick_query(pos_a-1);
}


////RURQ//////////////////////////////////////////////////////
long long B1[100001];long long B2[100001];
void base_update(long long *ft, int pos, long long value){
  //Add largest power of 2 dividing x / Last set bit in number x
  for (; pos <= N; pos += pos&(-pos))
    ft[pos] += value;
}
void rurq_range_update(int a, int b,long long v){
  base_update(B1, a, v);
  base_update(B1, b + 1, -v);
  base_update(B2, a, v * (a-1));     
  base_update(B2, b + 1, -v * b);     
}
void rurq_point_update(int a, long long v){
    rurq_range_update(a,a,v);
}
long long base_query(long long *ft,int b){
  long long sum = 0; 
  for(; b > 0; b -= b&(-b))
    sum += ft[b];
  return sum;
}
// Return sum A[1...b]
long long rurq_query(int b){
  return base_query(B1, b) * b - base_query(B2, b);
}

//Return sum A[a...b]
long long rurq_range_query(int a,int b){
  return rurq_query(b) - rurq_query(a-1);
}

// Initialise
pair<data_type_1, data_type_2> variable;
// OR
pair<data_type_1, data_type_2> variable = make_pair(value1,value2);

// Store values
variable.first = value;
variable second = value;
// Retrieve values
cout <<variable first << " " << variable.second << endl;

//Nesting pairs
pair<int, pair<int, int> > a;
a.first = 5;
a.second.first = 6;
a.second.second = 7;

stack<int> s;

s.push(5); // push an element onto the stack - O(1)
s.pop(); // pop an element from the stack - O(1)
s.top(); // access the element at the top of the stack - O(1)
s.empty(); // whether stack is empty - O(1)

// Initialize
vector<data_type> v;

v.push_back(value); // Add element to back
v.pop_back() // Remove last element
v.clear(); // Remove all elements

v[index] // Return element of index
v.back(); // Return last element

v.size(); // Return Size of vector
v.empty() // Return boolean value of whether vector is empty

set<int> s; set<int>::iterator it; 
multiset<int> s; multiset<int>::iterator it; 

s.insert(10);

it = s.find(8)
it = s.upper_bound(7);
it = s.lower_bound(7);

s.erase(10); //Remove element from set
s.erase(it) //Can also use iterators

s.empty();
s.clear();

// to loop through a set
for(it = s.begin(); it != s.end(); it++)
    cout << *it << " "; // outputs 2 7 10

deque<int> d;

// access an element / modify an element (0-indexed as well) - O(1)
d[0] = 2; // change deque from {5, 10} to {2, 10}
d[0]; // returns a value of 2

d.back(); // get back (last) element - O(1)
d.front(); // get front (first) element - O(1)
d.clear() // Remove all elements

d.push_back(5); // add an element to the back - O(1)
d.push_front(10); // add an element to the front - O(1)

d.pop_back(); // remove the back (last) element - O(1)
d.pop_front(); // remove the front (first) element - O(1)

d.size(); //Return size
d.empty // Whether queue is empty

struct node { 
    int start, end, mid, val, lazyadd;
    node left, right;  
    
    node(int _s, int _e) {  
        //Range of values stored
        start = _s; end = _e; mid = (start+end)/2;  
        //Min value stored
        val = 0;  lazyadd = 0;
        if (start!=end) {
            left = new node(start,mid);
            right = new node(mid+1,end);  
        }  
    }
    
    int value(){
        if (start==end){
            val += lazyadd;lazyadd = 0;return val;
        }else{
            val += lazyadd;
            // Propagate Lazyadd
            right->lazyadd += lazyadd; 
            left->lazyadd += lazyadd;
            lazyadd = 0;
            return val;
        }
    }
            
    void addRange(int lower_bound, int upper_bound, int val_to_add){
        if (start == lower_bound && end == upper_bound){
            lazyadd += val_to_add;
        }else{ 
            if (lower_bound > mid){
                right->addRange(lower_bound, upper_bound, val_to_add);
            }else if (upper_bound <= mid){
                left->addRange(lower_bound, upper_bound, val_to_add);
            }else{
                left->addRange(lower_bound, mid, val_to_add);
                right->addRange(mid+1, upper_bound, val_to_add);
            }
            val = min(left->value(), right->value());
        }
    }
    
    // Update position to new_value // O(log N)
    void update(int pos, int new_val) { //position x to new value
        if (start==end) { val=new_val; return; }  
        if (pos>mid) right->update(pos, new_val);  
        if (pos<=mid) left->update(pos, new_val);
        val = min(left->val, right->val);  
    } 
    
    // Range Minimum Query // O(log N)
    int rangeMinimumQuery(int lower_bound, int upper_bound) {
        //cout<<"Node:"<<start<<" "<<end<<" "<<mid<<" "<<val<<endl;
        //If Query Range Corresponds////////////////
        if (start==lower_bound && end==upper_bound){
            return value();
        }
        //Query Right Tree if range only lies there
        else if (lower_bound > mid){
            return right->rangeMinimumQuery(lower_bound, upper_bound);
        }
        //Query Left Tree if range only lies there
        else if (upper_bound <= mid){
            return left->rangeMinimumQuery(lower_bound, upper_bound);
        }
        //Query both ranges as range spans both trees
        else{
            return min(left->rangeMinimumQuery(lower_bound, mid),right->rangeMinimumQuery(mid+1, upper_bound));
        }
        //End//////////////////////////////////////////
    }
    
} *root;

void init(int N){
    root = new node(0, N-1); // creates seg tree of size n
}    
void update(int P, int V){
    root->update(P,V);
}
int query(int A, int B){
    int val = root->rangeMinimumQuery(A,B);
    return val;
}