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Sudoku.cpp

@@ -0,0 +1,95 @@
+#include<iostream>
+#include<cmath>
+using namespace std;
+
+bool isSafe(int mat[][9],int i,int j,int no){
+
+
+	//Check for row and col
+	for(int k=0;k<9;k++){
+		if(mat[k][j]==no||mat[i][k]==no){
+			return false;
+		}
+	}
+	//check for subgrid
+
+	int sx = (i/3)*3;
+	int sy = (j/3)*3;
+
+	for(int x=sx; x<sx + 3;x++){
+		for(int y =sy;y<sy + 3;y++){
+			if(mat[x][y]==no){
+				return false;
+			}
+		}
+	}
+	return true;
+}
+
+
+
+
+bool solveSudoku(int mat[][9],int i,int j,int n){
+	//base case
+	if(i==n){
+		//print the solution later
+		for(int i=0;i<9;i++){
+			for(int j=0;j<9;j++){
+				cout<<mat[i][j]<<" ";
+			}
+			cout<<endl;
+		}
+
+		return true;
+	}
+
+	//rec case
+	if(j==n){
+		return solveSudoku(mat,i+1,0,n);
+	}
+
+	//skip  the prefilled cell
+	if(mat[i][j]!=0){
+		return solveSudoku(mat,i,j+1,n);
+	}
+
+	//cell to be filled
+	//try out all possibilites
+	for(int no=1;no<=n;no++){
+		//whether it is safe to place the number or not
+		if(isSafe(mat,i,j,no)){
+
+			mat[i][j] = no;
+			bool solveSubproblem = solveSudoku(mat,i,j+1,n);
+			if(solveSubproblem==true){
+				return true;
+			}
+		}
+
+	}
+	// if no option works, backtracking 
+	mat[i][j] = 0;
+	return false;
+}
+
+
+int main(){
+	int n = 9;
+	int mat[9][9] =
+        {{5,3,0,0,7,0,0,0,0},
+        {6,0,0,1,9,5,0,0,0},
+        {0,9,8,0,0,0,0,6,0},
+        {8,0,0,0,6,0,0,0,3},
+        {4,0,0,8,0,3,0,0,1},
+        {7,0,0,0,2,0,0,0,6},
+        {0,6,0,0,0,0,2,8,0},
+        {0,0,0,4,1,9,0,0,5},
+        {0,0,0,0,8,0,0,7,9}};
+
+
+        if(!solveSudoku(mat,0,0,n)){
+        	cout<<"No solution exists!";
+        }
+
+
+}