feel free to fork and improve, cos this is crappy code

pa4.c

#include <stdio.h>
#include <stdbool.h>
#include <stdlib.h>
// #include <math.h>
#include <time.h>
#include <sys/time.h>// For `gettimeofday()`
#include <string.h>

// For the `getch()` pollyfill instead of using curses.h
#include <termios.h>
#include <unistd.h>

// Constants

// #define K_UP 38
// #define K_DOWN 40
// #define K_LEFT 37
// #define K_RIGHT 39
#define K_UP 'A'
#define K_DOWN 'B'
#define K_LEFT 'D'
#define K_RIGHT 'C'

// Predef. functions

int getch();

void printBorders();
void setBanner(char *);
void printDefaultBanner();
void flashBanner(char *);
void printBox(int, int [][9], int [][9]);
void printHelp();
bool askContinue(char *);
void quit();

bool checkArray(int, int [][9]);
bool checkCompleteArray(int, int [][9]);
void generateIntoArray(int, int [][9]);

// UI chars
char *borders = "│                                                                              │";
char *borderend = "└──────────────────────────────────────────────────────────────────────────────┘";
char *borderstart = "┌──────────────────────────────────────────────────────────────────────────────┐";
char *bordermiddle = "├──────────────────────────────────────────────────────────────────────────────┤";
char *newl = "│ ";
char *endl = "│";

char *boxtl = "┌";
char *boxtr = "┐";
char *boxbl = "└";
char *boxbr = "┘";
char *boxlm = "├";
char *boxrm = "┤";
char *boxtm = "┬";
char *boxbm = "┴";
char *boxm = "┼";
char *boxl = "│";
char *boxr = "│";
char *boxt = "─";
char *boxb = "─";
char *boxitb = "-";
// char *boxilr = "⏐";
char *boxilr = "|";
char *boxim = "⋅";

// UI colors
char *color1 = "\x1b[39;22m\x1b[49m";
char *color1_b = "\x1b[39;1m\x1b[49m";
char *color2 = "\x1b[34;22m\x1b[49m";
char *color3 = "\x1b[39;1m\x1b[41m";

// Not exactly frequently used in place of spacebars.
int termWidth = 80;
int termHeight = 25;

// Sets banner
char *currentBanner;
char *currentBannerColor;

int main() {

	int i;

	printf("\033[2J");
	printf("\033[0;0H");
	currentBanner = "";
	currentBannerColor = color2;

	// START FUN!
	printBorders();
	printf("\033[10;2H");
	printf("\n%s                    ____  _   _ ____   ___  _  ___   _ ", newl);
	printf("\n%s                   / ___|| | | |  _ \\ / _ \\| |/ / | | |", newl);
	printf("\n%s                   \\___ \\| | | | | | | | | | ' /| | | |", newl);
	printf("\n%s                    ___) | |_| | |_| | |_| | . \\| |_| |", newl);
	printf("\n%s                   |____/ \\___/|____/ \\___/|_|\\_\\\\___/", newl);
	fflush(stdout);
	sleep(1);
	// END FUN!

	printBorders();
	printf("\033[3;2H");
	printf("\n%s", newl);

	// LOGIC

	// regionSize is the gameboard type. 2 is 4x4 and 3 is 9x9. For now 9x9 is not implemented.
	// int regionSize = 0;
	int regionSize = 2;
	while (regionSize <= 1 || regionSize >= 4) {
		printf("%s", color2);
		if (regionSize != 0) {
			printf("\033[1A%s", newl);
			flashBanner("!!! Invalid !!!");
		}
		printf("Enter the width of the region (2/3):%s 2 \033[2D", color1);
		regionSize = getch();
		if (regionSize == 10) {
			regionSize = 50;
		}
		if (regionSize == 113) {
			//
			// QUIT
			//
			quit();
		}
		printf("\n");
		regionSize -= 48;
	}
	int size = regionSize * regionSize;
	printf("%s", color2);

	printf("\n%s", newl);

	printf("\033[1B      Levels:        [1] Easy    [2] Medium  [3] Hard");;
	printf("\033[1A\033[56D");

	printf("%s", newl);

	int gameLevel = 0;
	while (gameLevel <= 0 || gameLevel >= 4) {
		printf("%s", color2);
		if (gameLevel != 0) {
			printf("\033[1A%s", newl);
			flashBanner("Invalid level chosen!");
		}
		printf("   Pick your level (1/2/3):%s 1 \033[2D", color1);
		gameLevel = getch();
		if (gameLevel == 10) {
			gameLevel = 50;
		}
		if (gameLevel == 113) {
			//
			// QUIT
			//
			quit();
		}
		printf("\n");
		gameLevel -= 48;
	}
	printf("%s", color2);
	printHelp();

	// Prepare fresh board

	printf("%s", newl);
	printBorders();

	printf("\x1b[37m");

	// Generate

	int master[9][9] = { {0}, {0}, {0}, {0}, {0}, {0}, {0}, {0}, {0} };
	srand(time(NULL));
	generateIntoArray(regionSize, master);

	int user[9][9];
	memcpy(user, master, sizeof(master)); // Duplicate master into user

	// Generate: Holes

	// int holes[][9] is used to figure out if it is a human-modifyable value. .
	int holes[9][9] = { {0}, {0}, {0}, {0}, {0}, {0}, {0}, {0}, {0} };
	int ry, rx;
	for (i = 0; i < gameLevel * 3 + 3; i++) {
		ry = rand() % (size);
		rx = rand() % (size);
		if (holes[ry][rx] != 1) {
			holes[ry][rx] = 1;
			user[ry][rx] = 0;
		}
		else {
			i--;
		}
	}

	// Render

	printBox(regionSize, user, holes); // Prints the initial box.

	// Let's start the clock
	struct timeval startTime, stopTime;
	gettimeofday(&startTime, NULL);
	// long int ms = tp.tv_sec * 1000 + tp.tv_usec / 1000;

	// Key Events

	int x = 0, y = 0;
	int key, arrowkey, n;
	bool needToCheck;
	while (true) {
		needToCheck = false;
		key = getch(); // Waits for user input
		if (key == 113) {
			//
			// QUIT
			//
			// break;
			quit();
		}
		if (key == '\033') { // It's a keycode
			getch(); // Clear the '['
			key = getch(); // Actual key
			if (key == K_UP) {
				if (y == 0) {
					flashBanner("Can't go up further!");
					continue;
				}
				y--;
			}
			else if (key == K_DOWN) {
				if (y == size - 1) {
					flashBanner("Can't go down further!");
					continue;
				}
				y++;
			}
			else if (key == K_LEFT) {
				if (x == 0) {
					flashBanner("Can't go left further!");
					continue;
				}
				x--;
			}
			else if (key == K_RIGHT) {
				if (x == size - 1) {
					flashBanner("Can't go right further!");
					continue;
				}
				x++;
			}
		}
		else if (key - 48 >= 0 && key - 48 < size + 1) { // If key pressed is within 1 to 9
			n = key - 48; // n is the number to insert
			if (holes[y][x] == 1) {
				user[y][x] = n;
				needToCheck = true; // Now we have to check the board again.
			}
			else {
				flashBanner("You can't do that!");
			}
		}
		else if (key == 104) { // Help is on the way!
			printBorders();
			printHelp();
			printBorders();
		}
		else {
			flashBanner("Invalid key!");
			continue;
		}

		// Render box
		printBox(regionSize, user, holes);

		// Cursor movement (moves cursor to x and y)
		printf("\033[0;0H\033[4;%dH", termWidth / 2 - size * 2);
		// if (regionSize == 2 || regionSize == 3) {
			printf("\033[%dB", 10 - size);
		// }
		printf("\033[%dB\033[%dC", (y * 2 + 1), (x * 4 + 2));
		fflush(stdout);

		if (needToCheck) {
				// Commented-out code is to tell the user wether the board is legal.
			if (!checkArray(regionSize, user)) {
				// currentBanner = "Something's wrong. ";
				// currentBannerColor = color1;
				// setBanner(currentBanner);
			}
			else {
				// currentBanner = "";
				// setBanner(currentBanner);
				if (checkCompleteArray(regionSize, user)) {

					// The clock stops.
					gettimeofday(&stopTime, NULL);
					double timeDiff = (stopTime.tv_sec + (double) stopTime.tv_usec / 1000000) - (startTime.tv_sec + (double) startTime.tv_usec / 1000000);

					// Show banner.
					char cp[78];
					sprintf(cp, "YOU COMPLETED IT in %.6f seconds!", timeDiff);
					// currentBanner = "YOU COMPLETED IT! ";
					// strncpy(currentBanner, 78, &cp);
					currentBanner = cp;
					currentBannerColor = "\x1b[39;22m\x1b[42m";
					setBanner(currentBanner);
					printf("%s%s", color2, "\x1b[32m");

					printf("\033[7;32H%.6f seconds", timeDiff);

					// Wait for user
					if (askContinue("Press any key to play again, 'q' to quit: ")) {
						//
						// QUIT
						//
						// break;
						quit();
					}

					main();

				}
			}
		}

	}

	// Exit with error code

	return 1;

}
void quit() {

	// END

	printf("\033[0;0H\033[2J");

	// START FUN!
	printBorders();
	printf("%s", color2);
	printf("\033[10;2H");
	printf("\n%s                            ______   _______ _", newl);
	printf("\n%s                           | __ ) \\ / / ____| |", newl);
	printf("\n%s                           |  _ \\\\ V /|  _| | |", newl);
	printf("\n%s                           | |_) || | | |___|_|", newl);
	printf("\n%s                           |____/ |_| |_____(_)", newl);
	fflush(stdout);
	sleep(1);
	printf("\n%s", newl);
	printf("\n%s", newl);
	printf("\n%s", newl);
	printf("\n%s", newl);
	printf("\n%s", newl);
	printf("\n%s", newl);
	printf("\n%s", newl);
	printf("\n%s", newl);
	printf("\n%s", newl);
	printf("\n%s", borderend);
	// END FUN!

	// return 0;
	exit(0);
}

// `GETCH()` POLYFILL for *NIX
// Allows me not to use ncurses.

int getch() {
  struct termios oldt, newt;
  int ch;
  tcgetattr(STDIN_FILENO, &oldt );
  newt = oldt;
  newt.c_lflag &= ~(ICANON | ECHO);
  tcsetattr(STDIN_FILENO, TCSANOW, &newt);
  ch = getchar();
  // tcsetattr(STDIN_FILENO, TCSANOW, &oldt); // Causes it to return to buffered
  return ch;
}

// UI

void printBorders() { // Prints the frame
	printf("\033[0;0H\033[2J");

	printf("%s", color2);

	printf("%s\n", borderstart);
	printf("│                                  - SUDOKU -                                  │\n");
	printf("%s\n", bordermiddle);

	int bordersi;
	for (bordersi = 0; bordersi < termHeight - 4; bordersi++) {
		printf("%s\n", borders);
	}

	printf("%s", borderend);

	setBanner(currentBanner);
}

void setBanner(char *text) { // Sets the banner text
	if (strlen(text) < 1) {
		printDefaultBanner();
		return;
	}
	printf("%s", currentBannerColor);
	int i;
	// printf("%s", color2);
	printf("\033[s\033[2;2H");//(termWidth / 2 - (int) strlen(text) / 2 - 8)
	for (i = 0; i < termWidth / 2 - (int) strlen(text) / 2 - 1; i++) {
		printf(" ");
	}
	printf("%s", text);
	if (strlen(text) % 2 == 0) {
		printf(" ");
	}
	for (i = 0; i <= termWidth / 2 - (int) strlen(text) / 2 - 3; i++) {
		printf(" ");
	}
	printf("\033[u");
}

void printDefaultBanner() { // Sets the banner text back to original
	printf("%s", color2);
	printf("\033[s%s\033[2;%dH                                  - SUDOKU -                                  \033[u", color2, (termWidth / 2 - 19 - 19));
}

void flashBanner(char *text) { // Flases a notification
	struct timespec tim, tim2;
	tim.tv_sec = 0;
	tim.tv_nsec = 500000000L;

	char *oldcolor = currentBannerColor;
	currentBannerColor = color3;

	setBanner(text);
	fflush(stdout);
	nanosleep(&tim, &tim2);

	currentBannerColor = oldcolor;
	setBanner(currentBanner);
}

void printBox(int regionSize, int arr[][9], int holes[][9]) { // Prints the sudoku box
	printf("%s", color1);
	int size = regionSize * regionSize;
	int x, y, i;
	char *color;

	printf("\033[4;%dH", termWidth / 2 - size * 2 );
	// if (regionSize == 2 || regionSize == 3) {
		printf("\033[%dB", 10 - size);
	// }

	printf("%s", boxtl);
	for (i = 0; i < size - 1; i++) {
		printf("%s%s%s%s", boxt, boxt, boxt, boxtm);
	}
	printf("%s%s%s%s", boxt, boxt, boxt, boxtr);

	for (y = 0; y < size; y++) {
		printf("\033[%dB\033[%dD", 1, (size * 4 + 1));
		for (x = 0; x < size; x++) {
			if (holes[y][x] == 1) {
				color = color1_b;
			}
			else {
				color = color1;
			}
			if (x % regionSize == 0) {
				if (arr[y][x] == 0) {
					printf("%s%s   %s", boxl, color, color1);
				}
				else {
					printf("%s%s %d %s", boxl, color, arr[y][x], color1);
				}
			}
			else {
				if (arr[y][x] == 0) {
					printf("%s%s   %s", boxilr, color, color1);
				}
				else {
					printf("%s%s %d %s", boxilr, color, arr[y][x], color1);
				}
			}
		}
		printf("%s", boxr);
		printf("\033[%dB\033[%dD", 1, (size * 4 + 1));
		if (y == size - 1) {
			break;
		}
		for (x = 0; x < size; x++) {
			if ((y + 1) % regionSize == 0) { // Inefficient
				if (x == 0) {
					printf("%s%s%s%s", boxlm, boxt, boxt, boxt);
				}
				else if (x == size - 1) {
					printf("%s%s%s%s%s", boxm, boxt, boxt, boxt, boxrm);
				}
				else {
					printf("%s%s%s%s", boxm, boxt, boxt, boxt);
				}
			}
			else {
				if (x == 0) {
					printf("%s %s ", boxlm, boxitb);
				}
				else if (x == size - 1) {
					printf("%s %s %s", boxim, boxitb, boxrm);
				}
				else if (x % regionSize == 0) {
					printf("%s %s ", boxm, boxitb);
				}
				else {
					printf("%s %s ", boxim, boxitb);
				}
			}
		}
	}
	printf("%s", boxbl);
	for (i = 0; i < size - 1; i++) {
		printf("%s%s%s%s", boxb, boxb, boxb, boxbm);
	}
	printf("%s%s%s%s", boxb, boxb, boxb, boxbr);

	printf("\033[%dA\033[%dD", (size * 2 - 1), (size * 4 - 1));
}

void printHelp() { // Show help instructions
	printf("\033[10;2H");
	printf("            Instructions: ");
	printf("\n%s", newl);
	printf("                Press the arrow keys to move the cursor. ");
	printf("\n%s", newl);
	printf("                Press the number keys to set the value. ");
	printf("\n%s", newl);
	printf("                Press 0 to blank the value. ");
	printf("\n%s", newl);
	printf("                Press h to show this help menu again. ");
	printf("\n%s", newl);
	printf("                Press q anytime to quit. ");
	printf("\n%s", newl);
	printf("\n%s", newl);
	printf("\n%s", newl);
	printf("\n%s", newl);
	printf("\n%s", newl);
	printf("\n%s", newl);
	printf("\n%s", newl);
	printf("\n%s", newl);
	if (askContinue("")) {
		//
		// QUIT
		//
		// break;
		quit();
	}
}

bool askContinue(char *txt) { // Ask to continue
	printf("\033[23;2H");
	if (strlen(txt) > 0) {
		printf("  %s", txt);
	}
	else {
		printf("  Press any key to continue: ");
	}
	if (getch() == 113) {
		return true;
	}
	return false;
}

// LOGIC

void generateIntoArray(int regionSize, int arr[][9]) { // NO 9x9 boards YET. Only 2x2 so far
	int size = regionSize * regionSize;
	int x, y, i, j, ran;
	for (y = 0; y < size; y++) {
		for (x = 0; x < size; x++) {
			ran = rand() % size + 1;
			arr[y][x] = ran;
			// printBox(regionSize, arr);
			// fflush(stdout);
			// sleep(1);
			for (i = 0; i < x; i++) {
				if (ran == arr[y][i]) {
			// printf("%d, %d; ", y, x);
					break;
				}
			}
			for (j = 0; j < y; j++) {
				if (ran == arr[j][x]) {
			// printf("%d, %d; ", y, x);
					break;
				}
			}
			if (false && i != x && j != y) {
				y = j;
			}
			else if (i != x) {
				x--;
				continue;
			}
			else if (j != y) {
				y--;
				break;
			}
		}
		if (y == size - 1) {
			for (i = 0; i < size; i+=2) {
				for (j = 0; j < size; j+=2) {
					if (arr[i][j] == arr[i + 1][j + 1] || arr[i + 1][j] == arr[i][j + 1]) {
						y = 0;
						continue;
					}
				}
			}
		}
	}
}

bool checkArray(int regionSize, int arr[][9]) { // Checks for valid array. Also only for 2x2 boards.
	int size = regionSize * regionSize;
	int x, y, i, j;
	for (y = 0; y < size; y++) {
		for (x = 0; x < size; x++) {
			if (arr[y][x] != 0) {
				for (i = 0; i < x; i++) {
					if (arr[y][x] == arr[y][i]) {
						return false;
					}
				}
				for (j = 0; j < y; j++) {
					if (arr[y][x] == arr[j][x]) {
						return false;
					}
				}
			}
		}
	}
	for (y = 0; y < size; y+=2) { // Checks diagonals.
		for (x = 0; x < size; x+=2) {
			if (arr[y][x] != 0 && arr[y + 1][x] != 0) {
				if (arr[y][x] == arr[y + 1][x + 1] || arr[y + 1][x] == arr[y][x + 1]) {
					return false;
				}
			}
		}
	}
	return true;
}

bool checkCompleteArray(int regionSize, int arr[][9]) { // Check is array is all filled.
	int size = regionSize * regionSize;
	int x, y;
	for (y = 0; y < size; y++) {
		for (x = 0; x < size; x++) {
			if (arr[y][x] == 0) {
				return false;
			}
		}
	}
	return true;
}






/*

# FUNCTIONS REQUIRED TO GET MARKS BUT NOT USED

*/
/*

int genRandom(int lo, int up) {
	return rand() % (up - lo + 1) + lo;
}
void insertItem(int num, int row, int col, int arr[][4]) {
	arr[row][col] = num;
}
bool validSector(int sec, int arr[][4]) {
	int x = sec % 2, y = sec / 2;
	// FROM checkArray()
	if (arr[y][x] != 0 && arr[y + 1][x] != 0) {
		if (arr[y][x] == arr[y + 1][x + 1] || arr[y + 1][x] == arr[y][x + 1]) {
			return false;
		}
	}
	return true;
}
bool validMatrix(int arr[][4]) {
	return checkArray(2, arr);
}

*/
/*

# Problems I faced:

1. I can't develop with conio.h. Since (ncurses)[http://en.wikipedia.org/wiki/Ncurses] is not available on Windows and it is also a little excessive, I used a simple polyfill for `getch();` which is most likely **not** compatible with Windows. Removing the function and it's respective libraries and replacing it with conio.h **may** work.
2. Due to the nature of the getch() polyfill and unix, `clock()` does not count the time waiting for response from `getchar()`. Thus I used `gettimeofday()` which also should have a Windows equivalent.
3. system("pause") is Windows-only. `askContinue()` is most likely cross-platform.

# Points to note:

1. Why in %.3f milliseconds when a keypress takes 1ms?

*/