From f89d9051c71a5b5c0aebebec36dcc7cc63042b48 Mon Sep 17 00:00:00 2001
From: harjot3200 <harjot3200@gmail.com>
Date: Sun, 1 Oct 2017 12:47:28 +0530
Subject: [PATCH] Solver for sudoku

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

diff --git a/Backtracking/sudoku_solve.cpp b/Backtracking/sudoku_solve.cpp
new file mode 100644
index 000000000..e1e008a91
--- /dev/null
+++ b/Backtracking/sudoku_solve.cpp
@@ -0,0 +1,102 @@
+#include<iostream>
+using namespace std;
+///N=9;
+int n=9;
+
+
+bool isPossible(int mat[][9],int i,int j,int no){
+    ///Row or col nahin hona chahiye
+    for(int x=0;x<n;x++){
+        if(mat[x][j]==no||mat[i][x]==no){
+            return false;
+        }
+    }
+
+    /// Subgrid mein nahi hona chahiye
+    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;
+}
+void printMat(int mat[][9]){
+
+    for(int i=0;i<n;i++){
+        for(int j=0;j<n;j++){
+            cout<<mat[i][j]<<" ";
+            if((j+1)%3==0){
+                cout<<'\t';
+            }
+
+        }
+         if((i+1)%3==0){
+                cout<<endl;
+        }
+            cout<<endl;
+    }
+}
+
+
+bool solveSudoku(int mat[][9],int i,int j){
+    ///Base Case
+    if(i==9){
+        ///Solve kr chuke hain for 9 rows already
+        printMat(mat);
+        return true;
+    }
+
+    ///Crossed the last  Cell in the row
+    if(j==9){
+        return solveSudoku(mat,i+1,0);
+    }
+
+    ///Blue Cell - Skip
+    if(mat[i][j]!=0){
+        return solveSudoku(mat,i,j+1);
+    }
+    ///White Cell
+    ///Try to place every possible no
+    for(int no=1;no<=9;no++){
+        if(isPossible(mat,i,j,no)){
+            ///Place the no - assuming solution aa jayega
+            mat[i][j] = no;
+            bool aageKiSolveHui = solveSudoku(mat,i,j+1);
+            if(aageKiSolveHui){
+                return true;
+            }
+            ///Nahin solve hui
+            ///loop will place the next no.
+        }
+    }
+    ///Sare no try kr liey, kisi se bhi solve nahi hui
+    mat[i][j] = 0;
+    return false;
+}
+
+int main(){
+
+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}};
+
+printMat(mat);
+cout<<"Solution "<<endl;
+solveSudoku(mat,0,0);
+
+
+return 0;
+}