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Competitive Programming & Systems

C++ STL (Standard Template Library) Cheat Sheet

Quick syntax reference for vectors, maps, heaps, and algorithms in C++20. Run and inspect snippets directly in the ZenCompiler GCC 13 sandbox.

std::vector (Dynamic Array)

Dynamic array with contiguous storage, amortized O(1) push_back.

Run in C++ Sandbox
#include <iostream>
#include <vector>
#include <algorithm>

int main() {
    std::vector<int> v = {4, 1, 8, 3, 2};
    v.push_back(10);
    
    // Sort in ascending order
    std::sort(v.begin(), v.end());
    
    for (int x : v) {
        std::cout << x << " ";
    }
    std::cout << std::endl;
    return 0;
}

std::map & std::unordered_map

Associative key-value containers. map (Red-Black Tree O(log N)), unordered_map (Hash Table O(1)).

Run in C++ Sandbox
#include <iostream>
#include <unordered_map>
#include <string>

int main() {
    std::unordered_map<std::string, int> freq;
    std::string words[] = {"apple", "banana", "apple", "cherry", "banana", "apple"};
    
    for (const auto& w : words) {
        freq[w]++;
    }
    
    for (const auto& [word, count] : freq) {
        std::cout << word << ": " << count << std::endl;
    }
    return 0;
}

std::priority_queue (Max & Min Heap)

Heap data structure for O(log N) push and O(1) top access.

Run in C++ Sandbox
#include <iostream>
#include <queue>
#include <vector>

int main() {
    // Default: Max-heap
    std::priority_queue<int> max_heap;
    max_heap.push(10);
    max_heap.push(30);
    max_heap.push(20);
    
    std::cout << "Max element: " << max_heap.top() << std::endl; // 30
    
    // Min-heap: greater<int>
    std::priority_queue<int, std::vector<int>, std::greater<int>> min_heap;
    min_heap.push(10);
    min_heap.push(30);
    min_heap.push(20);
    
    std::cout << "Min element: " << min_heap.top() << std::endl; // 10
    return 0;
}