c_cpp 跳蛙

Posted 2021-05-14

// The frog start at position -1, the river starts at position 0, the frog must go to position river size (path) or bigger
// Compile with c++11, e.g. in clang++: clang++ frog.cpp -std=c++11

#include <vector>
#include <iostream>
#include <tuple>

typedef std::vector<int> Path;
typedef std::vector<std::tuple<int, int> > Visited;

bool walk(const int pos, const int speed, const Path& path, Visited& visited, Visited& walking);

static int ts = 0;

int main() {
	Path path = {0, 1, 0, 0, 0, 1, 0, 0, 0, 1, 1, 1, 0, 0, 1, 0, 1};
	Visited visited;

	int pos = -1;
	int speed = 0;

	Visited walking;
	if (walk(pos, speed , path, visited, walking)) {
		std::cerr << "#ops: " << ts << std::endl;
		std::cerr << "***** " << walking.size() << " ***** " << std::endl;
		for (auto w: walking) {
			std::cerr << std::get<0>(w) << " " << std::get<1>(w) << std::endl;
		}
		return 0;
	}

	return 1;
}

bool walk(const int pos, const int speed, const Path& path, Visited& visited, Visited& walking) {
	ts++;

	if (std::find(visited.begin(), visited.end(), std::make_tuple(pos, speed)) != visited.end()) {
		return false;
	}
	visited.emplace_back(pos, speed);

	// Crossed the river
	if (pos >= (signed) (path.size())) {
		walking.push_back(std::make_tuple(pos, speed));
		return true;
	}

	// Is on some block?
	if (pos >= 0 && !path[pos]) {
		return false;
	}

	// Too far from the river
	if (pos <= (-10 * (signed) path.size())) {
		return false;
	}

	std::vector<Visited> walkings;

	Visited walking1;
	if (walk(pos + (speed + 1), speed + 1, path, visited, walking1)) {
		walkings.push_back(walking1);
	}

	Visited walking2;
	if (walk(pos + speed, speed, path, visited, walking2)) {
		walkings.push_back(walking2);
	}

	Visited walking3;
	if (walk(pos + (speed - 1), speed - 1, path, visited, walking3)) {
		walkings.push_back(walking3);
	}

	if (walkings.empty()) {
		return false;
	}

	std::sort(walkings.begin(), walkings.end(), [](Visited& a, Visited& b) {
		return a.size() < b.size();
	});

	walking = walkings[0];
	walking.push_back(std::make_tuple(pos, speed));

	return true;
}