leetcode c++ headers

leetcode_helpers.cc

#pragma GCC optimize("Ofast,unroll-loops")
#pragma GCC target("sse,sse2,sse3,ssse3,sse4,avx,mmx,abm,popcnt,tune=native")

int const _ = [] { ios::sync_with_stdio(false); cin.tie(nullptr); cout.tie(nullptr); return 0; } ();

template <class T> using vec = vector<T>;
using T = TreeNode;
using ll = long long;
using vi = vec<int>;

// auto __unsync_with_stdio = std::ios::sync_with_stdio(false);
// auto __uncin_tie = std::cin.tie(nullptr);

////////////////////////////////////////////////////////////////////////////////////

#pragma GCC optimize("O3,unroll-loops,Ofast")
#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx")
static const auto harsh = []() {
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
    cout.tie(nullptr);
    return 0;
}();

#define LC_HACK
#ifdef LC_HACK
const auto __ = []() {
  struct ___ { static void _() { std::ofstream("display_runtime.txt") << 0 << '\n'; } };
  std::atexit(&___::_);
  return 0;
}();
#endif

////////////////////////////////////////////////////////////////////////////////////

template <class T> using vec = vector<T>;

using T = TreeNode;
using T = ListNode;

using vvi = vector<vector<int>>;
using vvc = vector<vector<char>>;
using vi = vector<int>;
using str = string;
using pii = pair<int, int>;
using pis = pair<int, string>;
using vs = vector<string>;

// strigbuf
std::stringstream ss(std::string(reserve, '\0'));
string(ss.str());

// reading words
stringstream ss(s);
string word;
stack<string> stk;
while(ss >> word) stk.push(word);

// priority queue / heap
make_heap(p.begin(), p.end());
pop_heap(p.begin(), p.end());
push_heap(p.begin(), p.end());

using pi = pair<int, int>

priority_queue<int> max_heap; max_heap.top(); max_heap.pop(); max_heap.push(x);
priority_queue<pi, vector<pi>, greater<pi> > min_heap; // over pi.first

sort(v.begin(), v.end(), [](const T & a, const T & b) -> bool { return a.t > b.t; });

auto comp = []( adjist a, adjlist b ) { return a.second > b.second; };
priority_queue< adjlist_edge , vector<adjlist_edge>, decltype( comp ) >
     adjlist_pq( comp );

/// vector slices
vector<int> s = {10, 20, 30, 40, 50, 60};
vector<int> d(s.begin(), s.end() - 1); // vector copy

span sp(s); // since 0x20
span ss = sp.subspan(2, 5); // (offset, count)

https://usaco.guide/silver/custom-cpp-stl?lang=cpp (Optional) C++ Sets with Custom Comparators
https://stackoverflow.com/questions/3221812/how-to-sum-up-elements-of-a-c-vector
https://stackoverflow.com/questions/2462951/c-equivalent-of-stringbuffer-stringbuilder std::stringstream ss(std::string(reserve, '\0')); string(ss.str())
https://stackoverflow.com/questions/2067988/recursive-lambda-functions-in-c11 Recursive Lambdas
https://usaco.guide/general/lambda-funcs?lang=cpp
https://stackoverflow.com/questions/17663186/initializing-a-two-dimensional-stdvector 2D vectors init
https://stackoverflow.com/questions/5122804/how-to-sort-with-a-lambda sort(start, end, lambda -> bool)

make_heap(p.begin(), p.end()), pop_heap(p.begin(), p.end()), push_heap(p.begin(), p.end());

using pi = pair<int, int>
priority_queue<pi, vector<pi>, greater<pi> > pq;

sort(v.begin(), v.end(), [](const T & a, const T & b) -> bool { return a.t > b.t; });

auto comp = []( adjist a, adjlist b ) { return a.second > b.second; };
priority_queue< adjlist_edge , vector<adjlist_edge>, decltype( comp ) >
     adjlist_pq( comp );

https://stackoverflow.com/questions/19019252/create-n-element-constexpr-array-in-c11 constexpr array init

hash map with custom key:

struct pair_hash
{
    template <class T, class U>
    std::size_t operator()(std::pair<T, U> const& pair) const {
        return std::hash<T>()(pair.first) ^ std::hash<U>()(pair.second);
    }
};

std::unordered_map<std::pair<int, int>,  int, pair_hash> umap;

for array<int, X>:

struct array_hash
{
    template <class T, long unsigned int U>
    std::size_t operator()(array<T, U> const& a) const {
        std::size_t h = 0; for (auto i: a) h = h ^ std::hash<T>()(i); return h;
    }
};

prefix sums in c++

        const int kLimit = *max_element(potions.begin(), potions.end());

	// get freq array up to max potion (10^5 * 4 bytes ~ 0.5MB)
        vector<int> freq(kLimit + 1, 0);
        for (int p : potions) {
            freq[p]++;
        }

	// suffix sums
        partial_sum(freq.rbegin(), freq.rend(), freq.rbegin());