## Flipkart Interview Question for SDE1s

Country: India
Interview Type: In-Person

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0
of 0 vote

``````public static boolean solveSudoku(int[][] board){
if(board == null){
throw new NullPointerException("\"board\" may not be null");
}
Worker worker = new Worker(board);
return worker.work();
}

static class Worker{
int[][] board;
HashSet<Integer>[] rowSets;
HashSet<Integer>[] colSets;
HashSet<Integer>[][] sqrSets;

Worker(int[][] board){
this.board = board;
this.init();
}

void init(){
this.rowSets = new HashSet<Integer>[9];
this.colSets = new HashSet<Integer>[9];
for(int i = 0; i < 9; i++){
this.rowSets[i] = new HashSet<Integer>();
this.colSets[i] = new HashSet<Integer>();
for(int j = 1; j < 10; j++){
}
}
this.sqrSets = new HashSet<Integer>[3][3];
for(int x = 0; x < 3; x++){
for(int y = 0; y < 3; y++){
this.sqrSets[x][y] = new HashSet<Integer>();
for(int i = 1; i < 10; i++){
}
}
}
for(int x = 0; x < this.board.length; x++){
for(int y = 0; y < this.board[x].length; y++){
if(this.board[x][y] > 0){
this.setValue(x, y, this.board[x][y])
}
}
}
}

void setValue(int x, int y, int val){
this.board[x][y] = val;
Integer integerVal = new Integer(val);
this.rowSets[y].remove(integerVal);
this.colSets[x].remove(integerVal);
this.sqrSets[x/3][y/3].remove(integerVal);
}

void unsetValue(int x, int y){
Integer integerVal = new Integer(this.board[x][y]);
this.board[x][y] = 0;
}

HashSet<Integer> getPossibles(int x, int y){
HashSet<Integer> possibles = new HashSet<Integer> possibles;
for(Integer i : this.rowSets[x/3][y/3]){
if(this.colSets[x].contains(i) && this.rowSet[y].contains(i)){
}
}
return possibles;
}

boolean work(){
int minX = -1;
int minY = -1;
HashSet<Integer> bestSolutions = null;
int min = Integer.MAX_VALUE;
outer: for(int x = 0; x < 9; x++){
for(int y = 0; y < 9; y++){
if(this.board[x][y] == 0){
HashSet<Integer> possibleSolutions = getPossibles(x, y);
if(possibleSolutions.size() == 0){
return false;
}
else if(possibleSolutions.size() == 1){
bestSolutions = possibleSolutions;
minX = x;
minY = y;
break outer;
}
else if(possibleSolutions.size() < min){
minX = x;
minY = y;
min = possibleSolutions.size();
bestSolutions = possibleSolutions;
}
}
}
}
if(minX == -1 && minY == -1){
return true;
}
Iterator<Integer> iterator = bestSolutions.iterator();
while(iterator.hasNext()){
Integer val = iterator.next();
this.setValue(minX, minY, val);
if(this.work()){
return true;
}
this.unset(minX, minY);
}
return false;
}
}``````

Comment hidden because of low score. Click to expand.
0
of 0 vote

This solution tries to solve sodoku based of given input. It puts the sudoku in final proccessed state. If given data provided has a solution it will take it to deterministic state..

``````import java.security.InvalidParameterException;
import java.util.HashSet;
import java.util.Iterator;
import java.util.Scanner;

public class CCup_5194452572307456 {
private static final int LEN = 9;
private final int MATLEN = (int) Math.sqrt(LEN);
private Cell[][] cells = new Cell[LEN][LEN];

class Cell {
public boolean done = false;
@SuppressWarnings("serial")
public HashSet<Byte> ele = new HashSet<Byte>() {
@Override
public String toString() {
Iterator<Byte> iter = ele.iterator();
StringBuilder builder = new StringBuilder();

builder.append("[");

while (iter.hasNext()) {
builder.append(iter.next());
if (iter.hasNext()) {
builder.append(",");
}
}

builder.append("]");

return builder.toString();
}
};
}

public CCup_5194452572307456(byte[][] board) {
if (board.length == LEN) {
for (byte[] inner : board) {
if (inner.length != LEN) {
throw new InvalidParameterException("Board length is not "
+ LEN);
}
}
} else {
throw new InvalidParameterException("Board length is not " + LEN);
}

init();

for (int x = 0; x < LEN; ++x) {
for (int y = 0; y < LEN; ++y) {
if (board[x][y] != 0) {
setValue(x, y, board[x][y]);
}
}
}
}

private void setValue(int x, int y, int value) {
cells[x][y].ele.clear();
cells[x][y].done = true;

for (int i = 0; i < LEN; ++i) {
if (i != y) {
cells[x][i].ele.remove((Byte) (byte) value);
}

if (i != x) {
cells[i][y].ele.remove((Byte) (byte) value);
}
}

int xx = x % MATLEN;
int yy = y % MATLEN;

x /= MATLEN;
y /= MATLEN;

for (int i = 0; i < MATLEN; ++i) {
for (int j = 0; j < MATLEN; ++j) {
if ((i != xx) || (j != yy)) {
cells[MATLEN * x + i][MATLEN * y + j].ele
.remove((Byte) (byte) value);
}
}
}
}

private void init() {
for (int i = 0; i < LEN; ++i) {
for (int j = 0; j < LEN; ++j) {
cells[i][j] = new Cell();
cells[i][j].done = false;

for (int k = 0; k < LEN; ++k) {
}
}
}
}

@Override
public String toString() {
StringBuilder builder = new StringBuilder();

for (int i = 0; i < LEN; ++i) {
for (int j = 0; j < LEN; ++j) {
builder.append(String.format("%1\$20s",
cells[i][j].ele.toString()
+ (cells[i][j].done ? "*" : "")));
}
builder.append(System.getProperty("line.separator"));
}

return builder.toString();
}

public static void main(String[] args) {
byte[][] data = new byte[CCup_5194452572307456.LEN][CCup_5194452572307456.LEN];
Scanner input = new Scanner(System.in);

System.out.println("Enter puzzle <Enter 0 for blank tiles>: ");
for (int i = 0; i < LEN; ++i) {
for (int j = 0; j < LEN; ++j) {
System.out.print("Enter coord [" + (i + 1) + "," + (j + 1)
+ "]: ");
data[i][j] = (byte) input.nextInt();
}
}

CCup_5194452572307456 cup = new CCup_5194452572307456(data);
cup.resolve();
System.out.println("Temp Solution: ");
System.out.println(cup);
input.close();
}

private void resolve() {
boolean yetToResolve = true;

while (yetToResolve) {
yetToResolve = false;

for (int i = 0; i < LEN; ++i) {
for (int j = 0; j < LEN; ++j) {
if ((!cells[i][j].done) && (cells[i][j].ele.size() == 1)) {
yetToResolve = true;
setValue(i, j, cells[i][j].ele.iterator().next());
}
}
}
}
}
}``````

Comment hidden because of low score. Click to expand.
0

you didn't handle the cases where there are no cells that can accommodate only 1 value. Hard sudokus need you to guess at some point. And that guessing would mimic a back-tracking algorithm.

Comment hidden because of low score. Click to expand.
0
of 0 vote

``````// A Backtracking program  in C++ to solve Sudoku problem
#include <stdio.h>

// UNASSIGNED is used for empty cells in sudoku grid
#define UNASSIGNED 0

// N is used for size of Sudoku grid. Size will be NxN
#define N 9

// This function finds an entry in grid that is still unassigned
bool FindUnassignedLocation(int grid[N][N], int &row, int &col);

// Checks whether it will be legal to assign num to the given row,col
bool isSafe(int grid[N][N], int row, int col, int num);

/* Takes a partially filled-in grid and attempts to assign values to
all unassigned locations in such a way to meet the requirements
for Sudoku solution (non-duplication across rows, columns, and boxes) */
bool SolveSudoku(int grid[N][N])
{
int row, col;

// If there is no unassigned location, we are done
if (!FindUnassignedLocation(grid, row, col))
return true; // success!

// consider digits 1 to 9
for (int num = 1; num <= 9; num++)
{
// if looks promising
if (isSafe(grid, row, col, num))
{
// make tentative assignment
grid[row][col] = num;

// return, if success, yay!
if (SolveSudoku(grid))
return true;

// failure, unmake & try again
grid[row][col] = UNASSIGNED;
}
}
return false; // this triggers backtracking
}

/* Searches the grid to find an entry that is still unassigned. If
found, the reference parameters row, col will be set the location
that is unassigned, and true is returned. If no unassigned entries
remain, false is returned. */
bool FindUnassignedLocation(int grid[N][N], int &row, int &col)
{
for (row = 0; row < N; row++)
for (col = 0; col < N; col++)
if (grid[row][col] == UNASSIGNED)
return true;
return false;
}

/* Returns a boolean which indicates whether any assigned entry
in the specified row matches the given number. */
bool UsedInRow(int grid[N][N], int row, int num)
{
for (int col = 0; col < N; col++)
if (grid[row][col] == num)
return true;
return false;
}

/* Returns a boolean which indicates whether any assigned entry
in the specified column matches the given number. */
bool UsedInCol(int grid[N][N], int col, int num)
{
for (int row = 0; row < N; row++)
if (grid[row][col] == num)
return true;
return false;
}

/* Returns a boolean which indicates whether any assigned entry
within the specified 3x3 box matches the given number. */
bool UsedInBox(int grid[N][N], int boxStartRow, int boxStartCol, int num)
{
for (int row = 0; row < 3; row++)
for (int col = 0; col < 3; col++)
if (grid[row+boxStartRow][col+boxStartCol] == num)
return true;
return false;
}

/* Returns a boolean which indicates whether it will be legal to assign
num to the given row,col location. */
bool isSafe(int grid[N][N], int row, int col, int num)
{
/* Check if 'num' is not already placed in current row,
current column and current 3x3 box */
return !UsedInRow(grid, row, num) &&
!UsedInCol(grid, col, num) &&
!UsedInBox(grid, row - row%3 , col - col%3, num);
}

/* A utility function to print grid  */
void printGrid(int grid[N][N])
{
for (int row = 0; row < N; row++)
{
for (int col = 0; col < N; col++)
printf("%2d", grid[row][col]);
printf("\n");
}
}

/* Driver Program to test above functions */
int main()
{
// 0 means unassigned cells
int grid[N][N] = {{3, 0, 6, 5, 0, 8, 4, 0, 0},
{5, 2, 0, 0, 0, 0, 0, 0, 0},
{0, 8, 7, 0, 0, 0, 0, 3, 1},
{0, 0, 3, 0, 1, 0, 0, 8, 0},
{9, 0, 0, 8, 6, 3, 0, 0, 5},
{0, 5, 0, 0, 9, 0, 6, 0, 0},
{1, 3, 0, 0, 0, 0, 2, 5, 0},
{0, 0, 0, 0, 0, 0, 0, 7, 4},
{0, 0, 5, 2, 0, 6, 3, 0, 0}};
if (SolveSudoku(grid) == true)
printGrid(grid);
else
printf("No solution exists");

return 0;
}``````

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