STL Containers & Algorithms

#include <iostream>
#include <vector>
#include <map>
#include <set>
#include <algorithm>
#include <numeric>
using namespace std;

int main() {
    // vector (dynamic array)
    vector<int> nums = {5, 2, 8, 1, 9, 3};
    nums.push_back(7);
    nums.emplace_back(4);  // Construct in-place (faster)

    // STL algorithms
    sort(nums.begin(), nums.end());
    auto it = find(nums.begin(), nums.end(), 8);
    if (it != nums.end()) cout << "Found 8 at index " << (it - nums.begin()) << endl;

    int total = accumulate(nums.begin(), nums.end(), 0);
    cout << "Sum: " << total << endl;

    // transform: apply function to each element
    vector<int> doubled(nums.size());
    transform(nums.begin(), nums.end(), doubled.begin(), [](int n) { return n * 2; });

    // map (ordered key-value pairs, O(log n))
    map<string, int> ages = {{"Alice", 30}, {"Bob", 25}};
    ages["Charlie"] = 35;
    ages.insert({"Diana", 28});

    for (const auto &[name, age] : ages) {  // Structured bindings (C++17)
        cout << name << ": " << age << endl;
    }

    // unordered_map (hash table, O(1) average)
    // #include <unordered_map>
    // Same API as map but faster for lookups

    // set (unique sorted elements)
    set<int> unique = {3, 1, 4, 1, 5, 9, 2, 6, 5};
    // Contains: {1, 2, 3, 4, 5, 6, 9} — duplicates removed, sorted

    // Check existence
    if (unique.count(4)) cout << "4 exists" << endl;
    if (unique.contains(4)) cout << "4 exists (C++20)" << endl;

    return 0;
}