Added n-queen and sudoku code

Author: PrachiSarda

Backtracking/Sudoku.cpp

@@ -0,0 +1,97 @@
+#include<iostream>
+using namespace std;
+int n=9;
+void printsudoku(int mat[][9])
+{
+    int i,j;
+    for(i=0;i<n;i++)
+    {
+        for(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 possible(int mat[][9],int i,int j,int no)
+{
+    int x,y;
+    for(x=0;x<n;x++)
+    {
+        if(mat[x][j]==no || mat[i][x]==no)
+        {
+            return false;
+        }
+    }
+    int m=(i/3)*3;
+    int p=(j/3)*3;
+    for(x=m;x<m+3;x++)
+    {
+        for(y=p;y<p+3;y++)
+        {
+            if(mat[x][y]==no)
+            {
+                return false;
+            }
+        }
+    }
+    return true;
+}
+bool solvesudoku(int mat[][9],int i,int j)
+{
+    if(i==9)
+    {
+        printsudoku(mat);
+        return true;
+    }
+
+    if (j==9)
+    {
+        return solvesudoku(mat,i+1,0);
+    }
+
+    if(mat[i][j]!=0)
+    {
+        return solvesudoku(mat,i,j+1);
+    }
+
+    for(int no=1;no<=9;no++)
+    {
+       if(possible(mat,i,j,no))
+       {
+           mat[i][j]=no;
+           bool aagekisolvehui=solvesudoku(mat,i,j+1);
+           if(aagekisolvehui)
+           {
+               return true;
+           }
+       }
+    }
+    mat[i][j]=0;
+    return false;
+}
+int main()
+{
+    int mat[][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}
+                 };
+
+    printsudoku(mat);
+    solvesudoku(mat,0,0);
+}

Backtracking/nQueen.cpp

@@ -0,0 +1,82 @@
+#include<iostream>
+using namespace std;
+bool safequeen(int board[][10],int i,int j,int n)
+{
+    for(int row=0;row<i;row++)
+    {
+        if(board[row][j]==1)
+        {
+            return false;
+        }
+    }
+
+    int x=i;
+    int y=j;
+    while(x>=0 && y>=0)
+    {
+        if(board[x][y]==1)
+        {
+            return false;
+        }
+        x--;
+        y--;
+    }
+
+    x=i;
+    y=j;
+    while(x>=0 && y<n)
+    {
+        if(board[x][y]==1)
+        {
+            return false;
+        }
+        x--;
+        y++;
+    }
+
+    return true;
+}
+bool nqueen(int board[][10],int i,int n)
+{
+    if(i==n)
+    {
+        for(int i=0;i<n;i++)
+        {
+            for(int j=0;j<n;j++)
+            {
+                if(board[i][j]==1)
+                {
+                    cout<<"Q";
+                }
+                else
+                {
+                    cout<<"_";
+                }
+            }
+            cout<<endl;
+        }
+        cout<<endl;
+        return false;
+    }
+    for(int j=0;j<n;j++)
+    {
+        if(safequeen(board,i,j,n))
+        {
+            board[i][j]=1;
+            if(nqueen(board,i+1,n))
+            {
+                return true;
+            }
+            board[i][j]=0;
+        }
+    }
+    return false;
+}
+int main()
+{
+    int n;
+    cin>>n;
+    int board[10][10]={0};
+    nqueen(board,0,n);
+    return 0;
+}