Merge branch 'master' of https://github.com/droconnel22/QuestionSet_Java

Author: droconnel22

src/main/java/com/hackerrank/dynamic/EightQueens.java

@@ -0,0 +1,114 @@
+package com.hackerrank.dynamic;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+
+/*
+
+stream of consciousness is key
+ok what can i do
+
+i have to recuserively search and check
+
+but what i don't understand is
+- is do i see the column? why?
+- why am i iterating..
+ */
+
+public class EightQueens {
+
+    private static final Integer SIZE = 8;
+
+    public static void main(String...args){
+        var e = new EightQueens();
+        var result = e.SolveEightQueens();
+        System.out.println(result.size());
+    }
+
+    List<int[]> SolveEightQueens(){
+        int[] columns = new int[]{0,0,0,0,0,0,0,0};
+        int row = 0;
+        List<int[]> solutions = new ArrayList<int[]>();
+        return solveEightQueens(columns,row,solutions);
+    }
+
+    private List<int[]> solveEightQueens(int[]columns, int row, List<int[]> solutions) {
+        // Start with bottom up base case
+        if(row == SIZE){
+            solutions.add(columns.clone());
+        } else {
+            // more rows to go
+            // each col has a unique queen that queen will have a number
+            for(int queen = 0; queen < SIZE; queen++) {
+                if(checkQueen(columns,row,queen)){
+                    // made it through check - place queen
+                    columns[row] = queen;
+                    solveEightQueens(columns,row+1,solutions);
+                }
+            }
+        }
+
+        return solutions;
+    }
+
+    /*
+    how do i check the row?
+    how do i check the col
+    how do i check the diagonal
+    keep thinking!!
+    your not thinking your just stalling
+
+    but I don't know what i am doing
+    what am i doing?
+    checking for unique values in a matrix
+    the x axis doesn't matter
+
+    only the position within the columns
+
+    what is the column value!??!?
+
+    why do i have to loop through the column
+
+    how do i critical think and problem solve?
+
+    Why!?
+     why is the key
+     you have a matrix of a board 8x8
+     queens must have unique row and column and also occupy a unique diagonal.
+     so it only matter one side
+     [1] 0
+     [2] 0
+     [3] 0
+     [4] 0
+     [5] 0
+     [6] 0
+     [7] 1
+     [8] 1
+     */
+
+    private boolean checkQueen(int[] columns, int proposedRowIndex, int proposedColIndex) {
+
+        // Bottom Up
+        for(int currentRow = 0; currentRow < proposedRowIndex; currentRow++){
+            int currentCol = columns[currentRow];
+            // Check Row
+            // there is no check because we go bottom up and so only consider empty rows.
+
+            // Check Column
+            if(currentCol == proposedColIndex){
+                return false;
+            }
+
+            // Check Diagonal
+            int columnDistance = Math.abs(proposedColIndex-currentCol);
+            int rowDistnace = currentRow-proposedRowIndex;
+            if(columnDistance == rowDistnace){
+                return false;
+            }
+
+        }
+        // if we get this far we made it
+        return true;
+    }
+}