Update 51. N-Queens

Author: khushi3004

51. N-Queens

@@ -2,46 +2,48 @@ class Solution {
     List<List<String>> result;
     public List<List<String>> solveNQueens(int n) {
         result = new ArrayList<>();
-        //Take a board. .Q
         char[][] board = new char[n][n];
-        for(int i =0; i < n; i++) {
+        
+        //Filled it as empty cells
+        for(int i = 0; i < n; i++){
             for(int j = 0; j < n; j++) {
                 board[i][j] = '.';
             }
         }
-        List<int[]> queenPos = new ArrayList<>();
-        dfs(board, 0, queenPos);
+        
+        List<int[]> queens = new ArrayList<>();
+        dfs(board, 0, queens);
         return result;
     }
 
-    private void dfs(char[][] board, int row, List<int[]> queenPos) {
-        //Chaeck if we have placed all the queens
-        if(queenPos.size() == board.length) {
-            //Construct the result
-            List<String> rowData = new ArrayList<>();
-            for(char[] c : board){
-                rowData.add(new String(c));
+    private void dfs(char[][] board, int r, List<int[]> queens) {
+        //Check if all queens are placed
+        if(queens.size() == board.length) {
+            //Construct output
+            List<String> rows = new ArrayList<>();
+            for(char[] row : board) {
+                rows.add(new String(row));
             }
-            result.add(rowData);
+            result.add(rows);
         }
 
-        //Try adduing Queen at row, col
-        for(int col = 0; col < board.length; col++) {
-            if(canAddQueen(queenPos, row, col)) {
-                board[row][col] = 'Q';
-                queenPos.add(new int[]{row, col});
-                dfs(board, row+1, queenPos);
-                board[row][col] = '.';
-                queenPos.remove(queenPos.size()-1);
+        //Try adding the queen
+        for(int c = 0; c < board.length; c++) {
+            if(canAddQueen(r,c,queens)) {
+                board[r][c] = 'Q';
+                queens.add(new int[]{r,c});
+                dfs(board, r+1, queens);
+                board[r][c] = '.';
+                queens.remove(queens.size()-1);
             }
         }
     }
 
-    private boolean canAddQueen(List<int[]> queenPos, int row, int col) {
-        for(int[] pair : queenPos) {
-            int dx = Math.abs(pair[0]- row);
-            int dy = Math.abs(pair[1]- col);
-            if(dx==0 || dy == 0 || dx == dy) return false;
+    private boolean canAddQueen(int r, int c, List<int[]> queens) {
+        for(int[] q : queens) {
+            int dx = Math.abs(r-q[0]);
+            int dy = Math.abs(c-q[1]);
+            if(dx==0 || dy==0 || dx==dy) return false;
         }
         return true;
     }