Java dsa-Backtracking

Backtracking/NQueen.java

@@ -0,0 +1,98 @@
+package Java_DSA.Backtracking;
+import java.util.*;
+
+public class NQueen
+{
+    public static void saveBoard(char[][] board,List<List<String>> allBoards){
+        String row = "";
+        List<String> newBoard = new ArrayList<>();
+        for (int i = 0;i < board.length;i++){
+            row = "";
+            for(int j = 0;j < board.length;j++){
+                if(board[i][j] == 'Q')
+                    row = row + 'Q';
+                else
+                    row = row + '.';
+            }
+            newBoard.add(row);
+        }
+        allBoards.add(newBoard);
+    }
+    public static boolean isSafe(int row,int col,char[][] board){
+        //checking horizontally
+        for(int j = 0;j < board.length;j++){
+            if(board[row][j] == 'Q'){
+                return false;
+            }
+        }
+
+        //checking verically
+        for(int i = 0;i < board.length;i++){
+            if(board[i][col] == 'Q'){
+                return false;
+            }
+        }
+
+        //checking upper left
+        int r = row;
+        for(int c = col;c >= 0 && r >= 0 ;c--,r--){
+            if(board[r][c] == 'Q'){
+                return false;
+            }
+        }
+
+        //checking upper right
+        r = row;
+        for(int c = col;c < board.length && r >= 0 ;c++,r--){
+            if(board[r][c] == 'Q'){
+                return false;
+            }
+        }
+
+        //checking lower left
+        r = row;
+        for(int c = col;c >= 0 && r < board.length ;c--,r++){
+            if(board[r][c] == 'Q'){
+                return false;
+            }
+        }
+
+        //checking lower right
+        r = row;
+        for(int c = col;c < board.length && r < board.length ;c++,r++){
+            if(board[r][c] == 'Q'){
+                return false;
+            }
+        }
+
+        return true;
+    }
+    public static void helper(char[][] board,List<List<String>> allBoards,int col){
+        if(col == board.length){
+            saveBoard(board,allBoards);
+            return;
+        }
+        for(int row = 0;row < board.length;row++){
+            if(isSafe(row,col,board)){
+                board[row][col] = 'Q';
+                helper(board,allBoards,col+1);
+                board[row][col] = '.';
+            }
+        }
+    }
+    public static List<List<String>>calcNQueen(int n){
+        List<List<String>>allBoards = new ArrayList<>();
+        char[][] board = new char[n][n];
+        helper(board,allBoards,0);
+
+        return allBoards;
+    }
+    public static void main(String[] args) {
+        Scanner sc = new Scanner(System.in);
+        List<List<String>> result = new ArrayList<>();
+        System.out.println("Enter the degree of the chess : ");
+        int n = sc.nextInt();
+        result = calcNQueen(n);
+        System.out.println(result);
+    }
+}

Backtracking/StringPermutation.java

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+package Java_DSA.Backtracking;
+
+public class StringPermutation {
+    public static void calcPermutation(String str,String perm,int index){
+        if(str.length() == 0){
+            System.out.println(perm);
+            return;
+        }
+        for(int i = 0;i < str.length();i++){
+            char currChar = str.charAt(i);
+            String newStr = str.substring(0,i) + str.substring(i+1);
+            calcPermutation(newStr,perm + currChar,index+1);
+        }
+    }
+    public static void main(String[] args) {
+        String str = "ABC";
+        calcPermutation(str,"",0);
+    }
+}