day 17

day17/Java/nQueen.java

@@ -0,0 +1,70 @@
+/*
+ * To change this license header, choose License Headers in Project Properties.
+ * To change this template file, choose Tools | Templates
+ * and open the template in the editor.
+ */
+package recursion;
+
+/**
+ * @date 14/01/19
+ * @author SPREEHA DUTTA
+ */
+import java.util.*;
+public class nQueen {
+    static int n;
+    public static void print(int arr[][])
+    {
+        for(int i=0;i<n;i++)
+        {
+            for(int j=0;j<n;j++)
+                System.out.print(arr[i][j]);
+            System.out.println();
+        }
+    }
+
+    public static boolean safe(int arr[][],int r,int c)
+    {
+        int i,j;
+        for(i=0;i<c;i++)
+            if(arr[r][i]==1)
+                return false;
+        for(i=r, j=c; i>=0 && j>=0; i--,j--)
+            if(arr[i][j]==1)
+                return false;
+        for(i=r, j=c; i<n && j>=0; i++,j--)
+            if(arr[i][j]==1)
+                return false;
+        return true;
+    }
+
+    public static boolean placeQueen(int arr[][],int c)
+    {
+        int i;
+        if(c>=n)
+            return true;
+        for(i=0;i<n;i++)
+        {
+            if(safe(arr,i,c))
+            {
+                arr[i][c]=1;
+                if(placeQueen(arr,c+1)==true)
+                    return true;
+                arr[i][c]=0;
+            }
+        }
+        return false;
+    }
+
+    public static void main(String []args)
+    {
+        Scanner sc=new Scanner(System.in);
+        n=sc.nextInt();
+        int arr[][]=new int[n][n];
+        if(placeQueen(arr,0)==false)
+        {
+            System.out.println("All the queens cannot be placed");
+        }
+        else
+            print(arr);
+    }
+}

day17/README.md

@@ -209,3 +209,73 @@ int main() {
    checkSolution();
 }
 ```
+
+## Java Implementation
+
+### [Solution](./Java/nQueen.java)
+
+```java
+/**
+ * @date 14/01/19
+ * @author SPREEHA DUTTA
+ */
+import java.util.*;
+public class nQueen {
+    static int n;
+    public static void print(int arr[][])
+    {
+        for(int i=0;i<n;i++)
+        {
+            for(int j=0;j<n;j++)
+                System.out.print(arr[i][j]);
+            System.out.println();
+        }
+    }
+
+    public static boolean safe(int arr[][],int r,int c)
+    {
+        int i,j;
+        for(i=0;i<c;i++)
+            if(arr[r][i]==1)
+                return false;
+        for(i=r, j=c; i>=0 && j>=0; i--,j--)
+            if(arr[i][j]==1)
+                return false;
+        for(i=r, j=c; i<n && j>=0; i++,j--)
+            if(arr[i][j]==1)
+                return false;
+        return true;
+    }
+
+    public static boolean placeQueen(int arr[][],int c)
+    {
+        int i;
+        if(c>=n)
+            return true;
+        for(i=0;i<n;i++)
+        {
+            if(safe(arr,i,c))
+            {
+                arr[i][c]=1;
+                if(placeQueen(arr,c+1)==true)
+                    return true;
+                arr[i][c]=0;
+            }
+        }
+        return false;
+    }
+
+    public static void main(String []args)
+    {
+        Scanner sc=new Scanner(System.in);
+        n=sc.nextInt();
+        int arr[][]=new int[n][n];
+        if(placeQueen(arr,0)==false)
+        {
+            System.out.println("All the queens cannot be placed");
+        }
+        else
+            print(arr);
+    }
+}
+```