From 3ffe4a788e27b1d93e80b66ed8c8091742d32447 Mon Sep 17 00:00:00 2001
From: Thunderb07t <kalpit29199@gmail.com>
Date: Tue, 29 Oct 2019 23:09:06 +0530
Subject: [PATCH] Added Sudoku Solver in C++ Programs folder.

---
 CPP/sudokuSolver.cpp | 102 +++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 102 insertions(+)
 create mode 100644 CPP/sudokuSolver.cpp

diff --git a/CPP/sudokuSolver.cpp b/CPP/sudokuSolver.cpp
new file mode 100644
index 0000000..2c01ea7
--- /dev/null
+++ b/CPP/sudokuSolver.cpp
@@ -0,0 +1,102 @@
+/*
+Input the sudoku where first input denotes the no of test cases.
+Then input a 2d 9X9 array , where 0 denotes an empty space.
+*/
+#include<bits/stdc++.h>
+using namespace std;
+bool canplace(int mat[][9],int i,int j,int n,int number)
+{
+	//  checking in row and column;
+	for(int x=0;x<n;x++)
+	{
+		if(mat[x][j]==number || mat[i][x]==number)
+		{
+			return false;
+		}
+	}
+
+	// checking in that particular block
+	int k=sqrt(n);
+	int RowStart= (i/k)*k;
+	int ColStart=(j/k)*k;
+
+	for(int p = RowStart ; p < (RowStart+k) ; p++)
+	{
+		for(int q = ColStart ; q < (ColStart+k) ; q++)
+		{
+			if(mat[p][q]==number)
+			{
+				return false;
+			}
+		}
+	}
+	return true;
+}
+void print(int mat[][9],int n)
+{
+	for(int i=0;i<n;i++)
+	{
+		for(int j=0;j<n;j++)
+		{
+			cout<<mat[i][j]<<" ";
+		}
+		cout<<endl;
+	}
+}
+bool sudokusolver(int mat[][9],int n,int i,int j)
+{
+	if(i==n)
+	{
+		print(mat,n);
+		cout<<endl;
+		return true;
+	}
+	// conditions
+	if(j==n)
+	{
+		return sudokusolver(mat,n,i+1,0);
+	}
+	if(mat[i][j]!=0)
+	{
+		return sudokusolver(mat,n,i,j+1);
+	}
+	// recursive case
+	for(int number=1;number<=n;number++)
+	{
+		if(canplace(mat,i,j,n,number))
+		{
+			// assume
+			mat[i][j]=number;
+			bool couldwesolve=sudokusolver(mat,n,i,j+1);
+			if(couldwesolve==true)
+			{
+				return true;
+			}
+		}
+	}
+
+	// backtrack here
+	mat[i][j]=0;
+	return false;
+}
+int main()
+{
+	int t;
+	cin>>t;
+	while(t--)
+	{
+	int n=9;
+	int mat[9][9];
+	for(int i=0;i<n;i++)
+	{
+		for(int j=0;j<n;j++)
+		{
+			cin>>mat[i][j];
+		}
+	}
+	cout<<endl;
+	sudokusolver(mat,n,0,0);
+	cout<<endl;
+	}
+	return 0;
+}