Language: C++

#define EXE
#ifdef EXE



// -------------------------------------------------------
#include <iostream>
#include <string>
#include <stdio.h>
#include <cassert>
#include <vector>
#include <algorithm>
using namespace std;

int min_steps = 10000;
int painted_offset = 10;

// string s;
int sx = 0;
int sy = 0;
int tx = 1;
int ty = 2;
#ifdef DEBUG

#else
cin >> sx >> sy >> tx >> ty;
#endif

vector<vector<int>> min_painted(20, vector<int>(20, -1));
string min_route;
void a(const int i0, const int j0, const int ax, const int ay, int now_steps, vector<vector<int>> painted, string route, int num, string direction) {
	now_steps++;
	route += direction;
	if (now_steps > min_steps) return;
	if (painted[i0 + painted_offset][j0 + painted_offset] != 9) {
		if (painted[i0 + painted_offset][j0 + painted_offset] != -1) {
			return;
		}
		painted[i0 + painted_offset][j0 + painted_offset] = num;
	}
	if (i0 == ax && j0 == ay) {
		//cout << "goal" << min_steps << " " << now_steps << " " << i0 << " " << j0 << endl;
		if (min_steps > now_steps)
		{
			min_steps = now_steps;
			min_painted = painted;
			min_route = route;
			//cout << i0 << " " << j0 << " " << min_steps << endl;
		}
		return;
	}
	int move_i, move_j;
	if (!num) {
		move_i = 0;
		move_j = 0;
	}
	else {
		move_i = -1;
		move_j = -1;
	}
	for (int i = move_i; i < 2; i++) {
		for (int j = move_j; j < 2; j++) {
			if (abs(i) == abs(j)) continue;
			if (painted[i0 + i + painted_offset][j0 + j + painted_offset] != -1 && painted[i0 + i + painted_offset][j0 + j + painted_offset] != 9) {
				continue;
			}

			if (abs(i0 + i) > 8 || abs(j0 + j) > 8) {
				continue;
			}
			if (num) {
				int tmp_i = i0 + i + painted_offset;
				int tmp_j = j0 + j + painted_offset;
				int num_neighbor_painted = 0;
				for (int ii = -1; ii < 2; ii++) {
					for (int jj = -1; jj < 2; jj++) {
						if (painted[tmp_i + ii][tmp_j + jj] != -1 && painted[tmp_i + ii][tmp_j + jj] != num)num_neighbor_painted++;
					}
				}

				if (!num_neighbor_painted) {
					continue;
				}

			}
			string next_direction;
			if (i == -1) {
				next_direction = "L";
			}
			else if (i == 1) {
				next_direction = "R";
			}
			else if (j == -1) {
				next_direction = "D";
			}
			else if (j == 1) {
				next_direction = "U";
			}
			else {
				assert(0);
			}

			a(i0 + i, j0 + j, ax, ay, now_steps, painted, route, num, next_direction);
		}
	}

	return;
}

int main() {


	vector<int> s{ sx, sy };
	vector<vector<int>> painted(20, vector<int>(20, -1));
	painted[painted_offset + sx][painted_offset + sy] = 9;
	painted[painted_offset + tx][painted_offset + ty] = 9;
	vector<int> t{ tx, ty };
	int now_steps = 0;
	string first_direction;
	a(sx, sy, tx, ty, now_steps, painted, min_route, 0, first_direction);
	if (0) {
		for (vector<int> painted_y : min_painted) {
			for (int painted_x : painted_y) {
				cout << painted_x << " ";
			}
			cout << endl;
		}
	}
	min_steps = 10000;
	a(tx, ty, sx, sy, now_steps, min_painted, min_route, 1, first_direction);

	if (0) {
		for (vector<int> painted_y : min_painted) {
			for (int painted_x : painted_y) {
				cout << painted_x << " ";
			}
			cout << endl;
		}
	}
	//std::cout << min_steps << endl;
	min_steps = 10000;
	a(sx, sy, tx, ty, now_steps, min_painted, min_route, 2, first_direction);
	min_steps = 10000;
	if (0) {
		for (vector<int> painted_y : min_painted) {
			for (int painted_x : painted_y) {
				cout << painted_x << " ";
			}
			cout << endl;
		}
	}
	min_steps = 10000;
	a(tx, ty, sx, sy, now_steps, min_painted, min_route, 3, first_direction);
	cout << min_route << endl;
	if (0) {
		for (vector<int> painted_y : min_painted) {
			for (int painted_x : painted_y) {
				cout << painted_x << " ";
			}
			cout << endl;
		}
	}

	//std::cout << min_steps << endl;



#ifdef DEBUG
	int z;
	cin >> z;
#endif
	return 0;
}


// -------------------------------------------------------
#endif

Compiler output:
a.cc:26:1: error: 'cin' does not name a type
   26 | cin >> sx >> sy >> tx >> ty;
      | ^~~