Merge pull request #1681 from a93a/51

Create 0051-n-queens-kt

Author: Ahmad-A0

kotlin/0051-n-queens.kt

@@ -0,0 +1,53 @@
+class Solution {
+    fun solveNQueens(n: Int): List<List<String>> {
+        val cols = HashSet<Int>() //keep track of used columns, we iterate rows
+        val posDia = HashSet<Int>() //...of positive diagonals R+C
+        val negDia = HashSet<Int>() //...of negative diagonals R-C
+        val temp: ArrayList<ArrayList<String>> = arrayListOf() // to hold our temporary distinct solution
+        val res: ArrayList<ArrayList<String>> = arrayListOf() // result with each distinct solutin where each input is a solution
+        fillWithQueens(0,n,res,cols,posDia,negDia,temp)
+        return res
+    }
+    private fun fillWithQueens(
+        row: Int, 
+        n: Int,
+        res: ArrayList<ArrayList<String>>, 
+        cols: HashSet<Int>, 
+        posDia: HashSet<Int>, 
+        negDia: HashSet<Int>,
+        board: ArrayList<ArrayList<String>>
+    ){
+        //if we have filled the whole board with queens
+        if(row == n){
+            val complete: ArrayList<String> = arrayListOf()
+            for(i in 0..n-1){
+                val joined = board[i].joinToString(separator = "")
+                complete.add(joined)
+            }
+            res.add(complete)
+            return
+        }
+        for(column in 0 until n){
+            if(cols.contains(column) || posDia.contains(row+column) || negDia.contains(row-column))
+                continue
+            val temp = tempRow(n)
+            board.add(temp)
+            cols.add(column)
+            posDia.add(row+column)
+            negDia.add(row-column)
+            board[row][column] = "Q"
+            fillWithQueens(row+1,n,res,cols,posDia,negDia,board)
+            cols.remove(column)
+            posDia.remove(row+column)
+            negDia.remove(row-column)
+            board[row][column] = "."
+        }
+    }
+    private fun tempRow(n: Int): ArrayList<String>{
+        val temp: ArrayList<String> = arrayListOf()
+        repeat(n){
+                temp.add(".")
+            }
+        return temp
+    }
+}