From 0e4cbb799c3f58931952676b3fa0be94fd2814f5 Mon Sep 17 00:00:00 2001
From: Vahagn Khachatryan <vkhachatrya5@bloomberg.net>
Date: Wed, 19 Aug 2020 22:13:39 +0100
Subject: [PATCH] Some training puzzles.

---
 .../training/max_points_on_a_line.cpp         | 116 ++++++++++++++
 .../training/multithreaded_queue.cpp          | 148 ++++++++++++++++++
 .../interviews/training/string_addition.cpp   |  84 ++++++++++
 3 files changed, 348 insertions(+)
 create mode 100644 puzzles/interviews/training/max_points_on_a_line.cpp
 create mode 100644 puzzles/interviews/training/multithreaded_queue.cpp
 create mode 100644 puzzles/interviews/training/string_addition.cpp

diff --git a/puzzles/interviews/training/max_points_on_a_line.cpp b/puzzles/interviews/training/max_points_on_a_line.cpp
new file mode 100644
index 0000000..a0e2788
--- /dev/null
+++ b/puzzles/interviews/training/max_points_on_a_line.cpp
@@ -0,0 +1,116 @@
+/*
+VIM: let b:lcppflags="-std=c++14 -O2 -pthread -I."
+VIM: let b:wcppflags="/O2 /EHsc /DWIN32"
+*/
+#include "stdafx.h"
+#include <iostream>
+#include <exception>
+#include <string>
+#include <chrono>
+#include <vector>
+#include <algorithm>
+#include <queue>
+#include <mutex>
+#include <condition_variable>
+#include <atomic>
+#include <unordered_map>
+#include <unordered_set>
+
+/*
+https://leetcode.com/problems/max-points-on-a-line/
+
+Given n points on a 2D plane, find the maximum number of points that lie on the same straight line.
+*/
+
+struct Point {
+	int x;
+	int y;
+	Point() : x(0), y(0) {}
+	Point(int a, int b) : x(a), y(b) {}
+};
+
+struct pairhash {
+	std::size_t operator() (const Point& p) const {
+		return std::hash<int>()(p.x) ^ std::hash<int>()(p.y);
+	}
+};
+
+bool operator == (const Point& p1, const Point& p2) {
+	return p1.x == p2.x && p1.y == p2.y;
+}
+
+Point ratio(int x, int y) {
+	if (x == 0) {
+		return Point(0, 1);
+	}
+	else if (y == 0) {
+		return Point(1, 0);
+	}
+	else if ( x < 0 ) {
+		x = -x;
+		y = -y;
+	}
+
+	int a = std::max(abs(x), abs(y));
+	int b = std::min(abs(x), abs(y));
+	for (int c; (c = a % b); a = b, b = c);
+	return Point(x / b, y / b);
+}
+
+int solve(const std::vector<Point>& v) {
+
+	std::unordered_map<Point, int, pairhash> vv;
+	for (const auto& p : v) {
+		vv[p]++;
+	}
+
+	if (vv.empty()) {
+		return 0;
+	}
+	else if (vv.size()==1) {
+		return vv.begin()->second;
+	}
+
+	int max_points = 1;
+	for (auto i = vv.begin(); i != vv.end(); i++) {
+		std::unordered_map<Point, int, pairhash> s;
+		for (auto j = std::next(i); j != vv.end(); j++) {
+			const auto line = ratio(i->first.x - j->first.x, i->first.y - j->first.y);
+			s[line] += j->second;
+			max_points = std::max(max_points, s[line] + i->second);
+		}
+	}
+
+	return max_points;
+}
+
+int main()
+{
+	try {
+		auto begin = std::chrono::high_resolution_clock::now();
+
+		std::cout << solve({ { 1,1 },{ 2,2 },{ 3,3 } }) << std::endl;
+		std::cout << solve({ { 1,1 },{ 3,2 },{ 5,3 },{ 4,1 },{ 2,3 },{ 1,4 } }) << std::endl;
+		std::cout << solve({ { 2, 3 },{ 3, 3 },{ -5, 3 } }) << std::endl;
+		std::cout << solve({ { 2, 2 },{ 3, 3 },{ 2, 2 },{ 3, 3 } }) << std::endl;
+		std::cout << solve({ { 2, 2 },{ 2, 3 },{ 3, 2 },{ 3, 3 } }) << std::endl;
+
+
+		auto end = std::chrono::high_resolution_clock::now();
+		std::chrono::duration<double> seconds = end - begin;
+		std::cout << "Time: " << seconds.count() << std::endl;
+		return 0;
+	}
+	catch (const std::exception& e)
+	{
+		std::cerr << std::endl
+			<< "std::exception(\"" << e.what() << "\")." << std::endl;
+		return 2;
+	}
+	catch (...)
+	{
+		std::cerr << std::endl
+			<< "unknown exception." << std::endl;
+		return 1;
+	}
+}
diff --git a/puzzles/interviews/training/multithreaded_queue.cpp b/puzzles/interviews/training/multithreaded_queue.cpp
new file mode 100644
index 0000000..6136b08
--- /dev/null
+++ b/puzzles/interviews/training/multithreaded_queue.cpp
@@ -0,0 +1,148 @@
+/*
+VIM: let b:lcppflags="-std=c++14 -O2 -pthread -I."
+VIM: let b:wcppflags="/O2 /EHsc /DWIN32"
+*/
+#include "stdafx.h"
+#include <iostream>
+#include <exception>
+#include <string>
+#include <chrono>
+#include <vector>
+#include <algorithm>
+#include <queue>
+#include <mutex>
+#include <condition_variable>
+#include <atomic>
+
+/*
+	Queue.
+*/
+
+thread_local size_t this_tid;
+
+template <typename M>
+class MtQueue {
+
+	std::queue<M> m_queue;
+	std::mutex m_mutex;
+	std::condition_variable m_push_cond;
+	std::condition_variable m_pop_cond;
+	std::atomic<bool> m_stopped;
+
+	static const size_t max_queue = 100;
+
+
+public:
+
+	/* Stop Queue */
+	void stop() {
+		std::unique_lock<std::mutex> lock(m_mutex);
+		m_stopped.store(true);
+		m_pop_cond.notify_all();
+		m_push_cond.notify_all();
+	}
+
+	/* Blocks when  */
+	bool push(M m) {
+		std::unique_lock<std::mutex> lock(m_mutex);
+		while (m_queue.size() >= max_queue && !m_stopped.load()) {
+			printf("                                            %lld: is full.\n", this_tid);
+			m_push_cond.wait(lock);
+		}
+		if (m_stopped.load()) {
+			return false;
+		}
+		m_queue.push(m);
+		printf("%lld: size %lld.\n", this_tid, m_queue.size());
+		m_pop_cond.notify_one();
+		return true;
+	}
+
+	/* Blocks when empty.*/
+	bool pop(M& m) {
+		std::unique_lock<std::mutex> lock(m_mutex);
+		while (m_queue.empty() && !m_stopped.load()) {
+			printf("                                            %lld: is empty.\n", this_tid);
+			m_pop_cond.wait(lock);
+		}
+		if (m_stopped.load()) {
+			return false;
+		}
+		m = m_queue.front();
+		m_queue.pop();
+		printf("%lld: size %lld.\n", this_tid, m_queue.size());
+		m_push_cond.notify_one();
+		return true;
+	}
+
+};
+
+void test() {
+	MtQueue<int> q;
+
+	auto push_proc = [&q](size_t tid) {
+		this_tid = tid;
+		int i = 0;
+		while (q.push(2)) {
+			if (++i % 101 == 0) {
+				auto m = std::chrono::milliseconds(100);
+				//printf("%lld: pusher waiting for %lldms.\n", this_tid, m.count());
+				//std::this_thread::sleep_for(m);
+			}
+		}
+	};
+	auto pop_proc = [&q](size_t tid) {
+		this_tid = tid;
+		int m;
+		while (q.pop(m)) {
+
+			//printf("%lld: popper waiting for %dms.\n", this_tid, m);
+			std::this_thread::sleep_for(std::chrono::milliseconds(m));
+		}
+	};
+
+
+	std::vector<std::thread> v;
+	v.reserve(16);
+	v.emplace_back(push_proc, v.size());
+	v.emplace_back(pop_proc, v.size());
+	v.emplace_back(pop_proc, v.size());
+	v.emplace_back(pop_proc, v.size());
+	v.emplace_back(pop_proc, v.size());
+	v.emplace_back(pop_proc, v.size());
+
+	std::this_thread::sleep_for(std::chrono::milliseconds(500));
+	q.stop();
+	printf("                                                                                   STOPPING.\n");
+	for (auto& t : v) {
+		t.join();
+	}
+}
+
+int main()
+{
+	try {
+		auto begin = std::chrono::high_resolution_clock::now();
+
+		while (true) {
+			test();
+		}
+
+		auto end = std::chrono::high_resolution_clock::now();
+		std::chrono::duration<double> seconds = end - begin;
+		std::cout << "Time: " << seconds.count() << std::endl;
+		return 0;
+	}
+	catch (const std::exception& e)
+	{
+		std::cerr << std::endl
+			<< "std::exception(\"" << e.what() << "\")." << std::endl;
+		return 2;
+	}
+	catch (...)
+	{
+		std::cerr << std::endl
+			<< "unknown exception." << std::endl;
+		return 1;
+	}
+}
diff --git a/puzzles/interviews/training/string_addition.cpp b/puzzles/interviews/training/string_addition.cpp
new file mode 100644
index 0000000..022a80c
--- /dev/null
+++ b/puzzles/interviews/training/string_addition.cpp
@@ -0,0 +1,84 @@
+/*
+VIM: let b:lcppflags="-std=c++14 -O2 -pthread -I."
+VIM: let b:wcppflags="/O2 /EHsc /DWIN32"
+*/
+#include "stdafx.h"
+#include <iostream>
+#include <exception>
+#include <string>
+#include <chrono>
+#include <vector>
+#include <algorithm>
+#include <queue>
+#include <mutex>
+#include <condition_variable>
+#include <atomic>
+
+/*
+	given an array representing a non-negative integer (ex: 123 represented
+	as [1,2,3]), return the next integer (output: [1,2,4]).
+	run through all edge cases (ex: [9,9,9,9,9,9,9,9] etc)
+*/
+
+int dig(char ch) {
+	return ch - '0';
+}
+
+char chr(int dig) {
+	return dig + '0';
+}
+
+std::string incr(std::string n) {
+	int carry = 1;
+	for (size_t i = n.size(); i-- > 0; ) {
+		int ds = dig(n[i]) + carry;
+		if (ds >= 10) {
+			carry = ds / 10;
+			ds %= 10;
+		}
+		else {
+			carry = 0;
+		}
+		n[i] = chr(ds);
+	}
+
+	if (carry) {
+		return chr(carry) + n;
+	}
+	else {
+		return n;
+	}
+}
+
+int main()
+{
+	try {
+		auto begin = std::chrono::high_resolution_clock::now();
+
+		std::cout << incr("0") << std::endl;
+		std::cout << incr("1") << std::endl;
+		std::cout << incr("9") << std::endl;
+		std::cout << incr("10") << std::endl;
+		std::cout << incr("15") << std::endl;
+		std::cout << incr("19") << std::endl;
+		std::cout << incr("99") << std::endl;
+		std::cout << incr("9999999") << std::endl;
+
+		auto end = std::chrono::high_resolution_clock::now();
+		std::chrono::duration<double> seconds = end - begin;
+		std::cout << "Time: " << seconds.count() << std::endl;
+		return 0;
+	}
+	catch (const std::exception& e)
+	{
+		std::cerr << std::endl
+			<< "std::exception(\"" << e.what() << "\")." << std::endl;
+		return 2;
+	}
+	catch (...)
+	{
+		std::cerr << std::endl
+			<< "unknown exception." << std::endl;
+		return 1;
+	}
+}