C++ comes with a lot of useful libraries we can use. In this section we will see some of them which are used very often in competitive programming. You can use this by using #include <bits/stdc++.h> in the top of your code.
Here are some of STL Algorithms.
int a[n]; sort(a, a + n); // Sort array of size n reverse(a, a + n); // Reverse the array *max_element(a, a + n); // returns the maximum element from 0 to n - 1 in a *min_element(a, a + n); // returns the minimum element from 0 to n - 1 in a accumulate(a, a + n, 0); // returns the sum of elements of a // If a is sorted then you can use this binary_search(a, a + n, x); // returns whether x is in a or not lower_bound(a, a + n, x); // returns an iterator to the first element greater or equal to x in a upper_bound(a, a + n, x); // returns an iterator to the first element greater to x in a
There are also a lot of useful built-in data structures, you can use. Here is an example:
queue<int> q; q.push(5); q.push(2); q.push(3); // Output it elements : 5 2 3 while (!q.empty()) { cout << q.front() << ' '; q.pop(); } cout << '\n'; stack<int> st; st.push(5); st.push(2); st.push(3); // Output it elements : 3 2 5 while (!st.empty()) { cout << st.top() << ' '; st.pop(); } cout << '\n'; vector<int> v; v.push_back(5); v.push_back(2); v.push_back(4); for (auto& e : v) cout << e << ' '; cout << '\n'; v.pop_back(); // pops the back of the element if it's not empty deque<int> dq; dq.push_back(5); dq.push_back(2); dq.push_front(4); // output the elements in the deque dq : 4 5 2 for (auto& e : dq) cout << e << ‘ ‘; dq.pop_back(); // pops the back of the element if it's not empty dq.pop_front(); // pops the front of the element if it's not empty set<int> s; s.insert(5); s.insert(2); s.insert(5); s.insert(1); // output it's size : 3 cout << s.size() << '\n'; // output elements in the set s : 1 2 5 for (auto& e : s) { cout << e << ' '; } s.find(x); // returns an iterator to the value x if there is x in s, and returns s.end() otherwise s.lower_bound(x); // returns an iterator to the first element greater or equal to x in s s.upper_bound(x); // returns an iterator to the first element greater to x in s s.erase(x); // erase the value x in s if there is any // note that this set is ordered by the smaller value (default) // you can change it to larger value with set<int, greater<int>> unoredered_set<int> us; us.insert(5); us.insert(2); us.insert(5); us.insert(1); // output it's size : 3 cout << us.size() << '\n'; // unoredered_set cannot be iterated like set multiset<int> ms; ms.insert(5); ms.insert(2); ms.insert(5); ms.insert(1); // output it's size : 4 cout << ms.size() << '\n'; // output the elements in the multiset ms : 1 2 5 5 for (auto& e : ms) { cout << e << ' '; } ms.find(x); // returns an iterator to the value x if there is x in ms, and returns ms.end() otherwise ms.lower_bound(x); // returns an iterator to the first element greater or equal to x in ms ms.upper_bound(x); // returns an iterator to the first element greater to x in ms ms.erase(x); // erase all the value x in ms if there is any ms.erase(ms.find(x)); // erase only one value x in ms if there is any map<int, int> mp; mp[5] = 2; mp[10] = 3; // output key and value pair for (auto e : mp) { cout << e.first << " " << e.second << '\n'; } mp.count(x); // equals to zero if x has not yet been a key value and one otherwise unordered_map<int, int> mp; // cannot be iterated, but faster to use when storing integers mp[5] = 2; mp[10] = 3; priority_queue<int> pq; pq.push(2); pq.push(5); pq.push(3); // output it's element : 5 3 2 while (!pq.empty()) { cout << pq.top() << " "; pq.pop(); } // Note that the default is storing the biggest element in the top // you can also configure it to smallest element first, by doing // priority_queue<int, vector<int>, greater<int>>
This is only an example, you can find on the internet yourself to know more about how to use the STL in C++. Usually, the best place to see it’s example is to go to cppreference, or just by simply googling it.