add n queens to readme.

.gitignore

@@ -1,9 +1,18 @@
+# out files
+*.out
+*.file
+
 # Java
 .class
 .jar
 
+# Perl
+nytprof*
+.callgrind
+
 # Python
 *.pyc
+*.lprof
 
 # Executables
 *.x

README.md

@@ -60,6 +60,9 @@ HTTP Server:
 Calculus: Simpson's Rule for Integration
 * Implements composite Simpson's Rule to integrate a function over an interval `[a,b]` using `n` approximating points
 
+N Queens:
+* Solve the N queens problem using integer arrays, with minimal object-oriented fluff.
+
 
 ### Programs In Progress
 
@@ -84,7 +87,7 @@ Arrays:
 * Use a native built-in data type to store a 1D array of data
 
 Matrix inversion:
-* Gauss-Jordan elimination algorithm
+* Gauss-Jordan elimination or back-substitution algorithm
 
 Vector products:
 * Given three three-dimensional vectors, compute dot/cross product, scalar/vector triple products

java/nqueens/NQueens.java

@@ -3,15 +3,20 @@ import java.util.Arrays;
 
 public class NQueens { 
 
+    public static final int SIZE = 9;
 
     ///////////////////////////////////////////////////
     // main 
     //
     public static void main(String[] args) {
+        long start = System.nanoTime();
         SolutionSaver s = new SolutionSaver();
-        Board b = new Board(8);
+        Board b = new Board(SIZE);
         explore(b,0);
+        long end = System.nanoTime();
+        long duration = end - start;
         System.out.printf("Found %d solutions\n ", SolutionSaver.nSolutions() );
+        System.out.printf("Elapsed time %03f s\n ", (duration/1E9) );
     }
     // 
     ///////////////////////////////////////////////////
@@ -20,25 +25,25 @@ public class NQueens {
     /// Placing queens, column-by-column; place the queen in column col. 
     public static void explore(Board b, int col) { 
 
-        if(col >= b.size() ) { 
+        if(col >= SIZE ) { 
 
             // We have reached the end.
             // No conflicts so far means no conflicts period.
 
             // Save solution in a static class, no instantiation overhead
-            String serial = b.toString();
-            SolutionSaver.saveSolution(serial);
+            SolutionSaver.saveSolution( b.toString() );
 
 		} else {
 
-            // The legalRows() method is a little bit of magic.
-            // It returns an array of valid rows on which to place the col^th queen.
-            for(Integer row : b.legalRows(col) ) { // important question: is this called each time in the loop?
-                                                   // (do i need to make a copy outside the loop?)
+            int[] attacked = b.getDiagAttacked(col);
+            int[] occupied = b.getOccupied(col);
+
+            for(int row=0; row<SIZE; row++) {
+                if(occupied[row]!=1 && attacked[row]!=1) { 
                     b.choose(row,col);
                     explore(b,col+1);
                     b.unchoose(row,col);
-
+                }
             }
         }// done with base/recursive cases
     }
@@ -55,7 +60,7 @@ class Board {
     int[] occupiedrows;             // Array to mark occupied rows.
                                     // This is how we check for horizontal attacks.
 
-    int board_size;                 // Size of our problem
+    public static int board_size;
 
     public Board(int size) {
         this.board_size = size;
@@ -63,11 +68,6 @@ class Board {
         this.occupiedrows = new int[size];
     }
 
-    /// Get board size
-    public int size(){ 
-        return this.board_size;
-    }
-
     /** 
      * Get String representation of queen positions.
      * This prints 8 numbers, corresponding to 8 columns.
@@ -95,52 +95,44 @@ class Board {
         }
     }
 
-    /// Get a list of legal rows
-    public LinkedList<Integer> legalRows( int col ) { 
+    /// Get a list of occupied rows
+    public int[] getOccupied(int col) {
+        return this.occupiedrows;
+    }
 
-        LinkedList<Integer> legalList = new LinkedList<Integer>();
+    /// Get a list of attacked diagonals
+    public int[] getDiagAttacked( int col ) { 
 
-        // 1. Mark invalid squares on diagonals of already-placed queens
+        // 1. Mark invalid squares on diagoonals of already-placed queens
         //
         // 2. For this column, loop over each row where it's legal to place a queen,
         //    and run backtracking on that choice. Then unmake the choice and keep going.
 
         // Store invalid rows on other queens' diagonals 
-        int[] diag = new int[size()];
+        int[] diag = new int[this.board_size];
 
         // Loop over all of the queens already placed (col-1)
         for(int k = 0; k <= (col-1); k++ ) {
 
             // We're gonig to place the next queen on col.
-            // Find which squares are on diagonal of queen k, 
+            // Find which squares are on diagonals of queen k, 
             // and mark them as impossible.
 
-            // Lower right diagonal
+            // Lower right diag
             int ix1 = this.queens[k] + col - k;
-            if(ix1 >= 0 && ix1 < size() ) {
+            if(ix1 >= 0 && ix1 < this.board_size ) {
                 diag[ix1] = 1;
             }
 
-            // Upper right diagonal
+            // Upper right diag
             int ix2 = this.queens[k] - col + k;
-            if(ix2 >= 0 && ix2 < size() ) {
+            if(ix2 >= 0 && ix2 < this.board_size ) {
                 diag[ix2] = 1;
             }
 
         }
 
-        // Legal rows are non-diagonal squares and squares on non-occupied rows.
-        for (int row = 0; row < size(); row++) {
-
-            // If this row is legal, add it to the list
-            boolean legal = diag[row]==0 && this.occupiedrows[row]==0;
-            if(legal) {
-                legalList.add(row);
-            }
-
-        }
-        
-        return legalList;
+        return diag;
     }
 }
 

java/nqueens/prof_java_hprof.sh

@@ -0,0 +1,30 @@
+#!/bin/sh
+#
+# Profile the N queens problem using Java Iteractive Profiler
+# http://jiprof.sourceforge.net/
+# 
+# Also see http://charlesreid1.com/wiki/Java/Profiling
+#
+# Download source and look for profile/profile.jar
+
+export PATH2JIP="${HOME}/Downloads/jip-src-1.2"
+
+for N in 14
+do
+
+    echo "**************************************"
+    echo "Profiling $N queens problem with Java JIP..."
+    
+    # Update N
+    /usr/local/bin/sed -i "s/SIZE = [0-9]\{1,\}/SIZE = ${N}/g" NQueens.java
+    
+    # Compile
+    javac NQueens.java
+    
+    java -javaagent:${PATH2JIP}/profile/profile.jar NQueens
+    
+    mv profile.txt profile_jip_${N}queens.out
+    tail -n30 profile_${N}queens.out
+
+done
+

java/nqueens/prof_java_jip.sh

@@ -0,0 +1,32 @@
+#!/bin/sh
+#
+# Profile the N queens problem using Java Iteractive Profiler
+# http://jiprof.sourceforge.net/
+# 
+# Also see http://charlesreid1.com/wiki/Java/Profiling
+#
+# Download source and look for profile/profile.jar
+
+for N in 14
+do
+
+    echo "**************************************"
+    echo "Profiling $N queens problem with Java HPROF..."
+    
+    # Update N
+    /usr/local/bin/sed -i "s/SIZE = [0-9]\{1,\}/SIZE = ${N}/g" NQueens.java
+    
+    # Compile
+    javac NQueens.java
+    
+    echo " - - - - - - - - - - - - - - - - - - - - -"
+    echo "Profiling $N queens with HPROF..."
+    
+    java -agentlib:hprof=verbose=n NQueens
+    #java -agentlib:hprof NQueens
+    #java -agentlib:hprof=cpu=samples NQueens
+    
+    mv java.hprof.txt profile_hprof_${N}queens.out
+    tail -n30 hprof_${N}queens.out
+done
+

java/nqueens/time_java.sh

@@ -0,0 +1,26 @@
+#!/bin/sh
+
+export RIGHTNOW="`date +"%Y%m%d_%H%M%S"`"
+export OUT="timeout_nqueens_java_${RIGHTNOW}.out"
+touch ${OUT}
+cat /dev/null > ${OUT}
+
+for N in 8 9 10 11 12 13 14 15
+do
+    echo "**************************************" >> ${OUT}
+    echo "Running $N queens problem with Java..." >> ${OUT}
+    
+    # Update N
+    /usr/local/bin/sed -i "s/SIZE = [0-9]\{1,\}/SIZE = ${N}/g" NQueens.java
+    
+    # Compile
+    javac Nqueens.java
+
+    # Semicolon is important here
+    echo "Running..."
+    { time java NQueens >> ${OUT}; } 2>> ${OUT}
+    echo "Done."
+
+    echo "" >> ${OUT}
+
+done

perl/99bottles.pl

@@ -1,4 +1,4 @@
-#!/usr/bin/perl -w
+#!/usr/local/bin/perl -w
  
 my $verse = <<"VERSE";
 100 bottles of beer on the wall,

perl/hello_world.pl

@@ -1,3 +1,3 @@
-#!/usr/bin/perl
+#!/usr/local/bin/perl
 
 print 'hello world';

perl/nqueens/nqueens.pl

@@ -0,0 +1,119 @@
+#!/usr/local/bin/perl
+use Time::HiRes qw(time);
+use strict;
+use warnings;
+my $start = time;
+
+######################################
+########## N Queens Puzzle ###########
+#
+# 
+# The 8 queens problem is to place 8 queens on a chessboard
+# such that no queen attacks any other queen.
+#
+# In 1972, Dijkstra published the first depth-first 
+# backtracking algorithm to solve the problem.
+#
+# This file implements a recursive backtracking algorithm
+# to find solutions to the N queens problem.
+# 
+# This requires a way of choosing queens, 
+# and a way to check if a configuration is valid (as we go).
+# The backtracking algorithm recursively calls a method 
+# to place one queen at a time, 8 times.
+# When there are no more choices left to make, it has reached a leaf,
+# and it stores (or prints out) a solution.
+#
+# Modified and expanded from http://rosettacode.org/wiki/N-queens_problem#Perl
+
+# Create an array to store solutions
+my @solutions;
+
+# Create an array to store where queens have been placed
+my @queens;
+
+# Mark the rows already used (useful for lookup)
+my @occupied;
+
+# Size of board
+my $board_size;
+
+
+# explore() implements a recursive, depth-first backtracking method
+sub explore { 
+	# Parameters:
+	#	depth : this is the argument passed by the user
+
+	# First argument passed to the function is $depth 
+	# (how many queens we've placed on the board),
+	# so use shift to pop that out of the parameters 
+	my ($depth, @attacked) = shift;
+
+	# Explore is a recursive method,
+	# so we need a base case and a recursive case.
+	#
+	# The base case is, we've reached a leaf node,
+	# placed 8 queens, and had no problems, 
+	# so we found a solution.
+	if ($depth==$board_size) { 
+		# Here, we store the stringified version of @queens,
+		# which are the row numbers of prior queens. 
+		# This is a global variable that is shared across
+		# instances of this recursive function.
+		push @solutions, "@queens\n";
+		return;
+	}
+
+
+    ##################################
+    # Method 1
+    #
+	# Mark the squares that are attackable, 
+	# so that we can cut down on the search space.
+    my($ix1, $ix2); 
+	$#attacked = 2 * $board_size;
+	for( 0 .. $#queens) { 
+		$ix1 = $queens[$_] + $depth - $_ ;
+		$attacked[ $ix1 ] = 1;
+
+		$ix2 = $queens[$_] - $depth + $_ ;
+		$attacked[ $ix2 ] = 1;
+	}
+    #
+    ####################################
+
+
+	for my $row (0 .. $board_size-1) {
+		# Cut down on the search space:
+		# if this square is already occupied
+		# or will lead to an invalid solution,
+		# don't bother exploring it.
+		next if $occupied[$row] || $attacked[$row];
+
+		# Make a choice
+		push @queens, $row;
+		# Mark the square as occupied
+		$occupied[$row] = 1;
+
+		# Explore the consequences
+		explore($depth+1);
+
+		# Unmake the choice
+		pop @queens;
+		
+		# Mark the square as unoccupied
+		$occupied[$row] = 0;
+
+	}
+}
+
+$board_size = 11; 
+
+explore(0);
+
+my $duration = time - $start;
+
+print "Found ", scalar(@solutions), " solutions\n";
+printf "Execution time: %0.3f s \n",$duration;
+
+

perl/nqueens/prof_perl.sh

@@ -0,0 +1,32 @@
+#!/bin/sh
+#
+# Profile the N queens problem using Devel::NYTProf
+#
+# Install using cpanm:
+# $ cpanm Devel::NYTProf
+#
+
+for N in 8 9 10 11 12
+do
+
+    echo "**************************************" 
+    echo "Profiling $N queens problem with Perl..."
+    
+    # Update N
+    /usr/local/bin/sed -i "s/board_size = [0-9]\{1,\};/board_size = ${N};/g" nqueens.pl
+    
+    echo "Running..."
+    /usr/local/bin/perl -d:NYTProf nqueens.pl
+    echo "Done."
+    
+    # CSV contains interesting info
+    ${HOME}/perl5/bin/nytprofcsv nytprof.out 
+
+    ## More information... 
+    #${HOME}/perl5/bin/nytprofcg nytprof.out 
+    #${HOME}/perl5/bin/nytprofhtml nytprof.out 
+
+    mv nytprof nytprof${N}
+
+done
+

perl/nqueens/time_perl.sh

@@ -0,0 +1,23 @@
+#!/bin/sh
+
+export RIGHTNOW="`date +"%Y%m%d_%H%M%S"`"
+export OUT="timeout_queens_perl_${RIGHTNOW}.out"
+touch ${OUT}
+cat /dev/null > ${OUT}
+
+for N in 8 9 10 11 12 13 14 15
+do
+    echo "**************************************" >> ${OUT}
+    echo "Running $N queens problem with Perl..." >> ${OUT}
+    
+    # Update N
+    /usr/local/bin/sed -i "s/board_size = [0-9]\{1,\};/board_size = ${N};/g" nqueens.pl
+    
+    # Semicolon is important here
+    echo "Running..."
+    { time /usr/local/bin/perl nqueens.pl >> ${OUT}; } 2>> ${OUT}
+    echo "Done."
+
+    echo "" >> ${OUT}
+
+done

python/nqueens/nqueens.py

@@ -1,12 +1,14 @@
 # Look ma, no modules!
 
 # bottlenecks around 12, when the problem size starts to mushroom
-board_size = 10
+board_size = 11
 
 solutions = []
 queens = []
 occupied = board_size*[0,]
 
+
+
 def explore(depth):
     # base case
     if(depth==board_size):

python/nqueens/prof_python_cprof.sh

@@ -0,0 +1,24 @@
+#!/bin/sh
+#
+# Profile the N queens problem using cProfile
+
+export RIGHTNOW="`date +"%Y%m%d_%H%M%S"`"
+export OUT="outfile_prof_nqueens_python_${RIGHTNOW}.out"
+
+for N in 8 9 10 11
+do
+
+    echo "**************************************" >> ${OUT}
+    echo "Profiling $N queens problem with Python..." >> ${OUT}
+    
+    # Update N
+    /usr/local/bin/sed -i "s/board_size = [0-9]\{1,\}/board_size = ${N}/g" nqueens.py
+
+    rm -f *.pyc
+    
+    echo "Running..."
+    python pycprof_nqueens.py >> ${OUT}
+    echo "Done."
+
+done
+

python/nqueens/prof_python_lineprof.sh

@@ -0,0 +1,36 @@
+#!/bin/sh
+#
+# Profile the N queens problem using cProfile
+
+export RIGHTNOW="`date +"%Y%m%d_%H%M%S"`"
+export OUT="outfile_prof_nqueens_python_${RIGHTNOW}.out"
+
+# Add function decorator
+/usr/local/bin/sed -i "s/def explore/@profile\ndef explore/g" nqueens.py
+
+for N in 8 9 10 11
+do
+
+    echo "**************************************" >> ${OUT}
+    echo "Profiling $N queens problem with Python..." >> ${OUT}
+    
+    # Update N
+    /usr/local/bin/sed -i "s/board_size = [0-9]\{1,\}/board_size = ${N}/g" nqueens.py
+
+    rm -f *.pyc
+    
+    echo "Running program via kernprof..."
+
+    # runs the program
+    kernprof -l nqueens.py >> ${OUT}
+
+    # results are in nqueens.py.lprof
+    python -m line_profiler nqueens.py.lprof >> ${OUT}
+
+    echo "Done."
+
+done
+
+# Remove function decorator
+/usr/local/bin/sed -i "s/@profile//g" nqueens.py
+

python/nqueens/pycprof_nqueens.py

@@ -0,0 +1,21 @@
+print "*******************************"
+print "cProfile:"
+print "*******************************"
+
+import pstats, StringIO
+import cProfile
+pr = cProfile.Profile()
+pr.enable()
+import nqueens
+pr.disable()
+
+## Simple
+#pr.dump_stats('stats.file')
+#pr.print_stats()
+
+# Complicated
+s = StringIO.StringIO()
+sortby = 'time'
+ps = pstats.Stats(pr, stream=s).sort_stats(sortby)
+ps.print_stats()
+print s.getvalue()

python/nqueens/time_python.sh

@@ -6,8 +6,8 @@ touch ${OUT}
 cat /dev/null > ${OUT}
 
 #for N in 8 9 10 11 12 13 14 15
-#for N in 8 9 10 11 12 
-for N in 13 14
+#for N in 12 13 14
+for N in 8 9 10 11
 do
     echo "**************************************" >> ${OUT}
     echo "Running $N queens problem with Python..." >> ${OUT}
@@ -15,6 +15,8 @@ do
     # Update N
     /usr/local/bin/sed -i "s/board_size = [0-9]\{1,\}/board_size = ${N}/g" nqueens.py 
 
+    rm -f *.pyc
+    
     # Semicolon is important here
     echo "Running..."
     { time python time_nqueens.py >> ${OUT}; } 2>> ${OUT}

python/profile_nqueens.py

@@ -1,7 +0,0 @@
-import cProfile
-pr = cProfile.Profile()
-pr.enable()
-import nqueens
-pr.disable()
-
-pr.print_stats()