Re^2: spiral path traversal for a grid

[serf]

Very literally and verbosely so you can see what it's doing:

#!/usr/bin/perl
#
# Matrix Spiral
#
use strict;
use warnings;

#
# Size of input matrix in columns and rows
#
my $cols = 7;
my $rows = 3;

#
# Decrement rows & columns because we're using them as array indices
# (i.e. counting from 0 not 1)
#
$cols--;
$rows--;


#
# Populate a list of elements to feed the matrix from
#
my @elements;

while (<DATA>) {

    #
    # Display data to screen so we can compare results to it
    #
    print;

    push @elements, (split(' ', $_));

}

#
# Keep the size of elements for after we've shifted it empty
#
my $count = @elements;

#
# Populate a matrix of the elements
# which pacman can then walk around & eat pill by pill...
#
my @matrix;

for my $row (0 .. $rows ) {

    for my $col (0 .. $cols ) {

        $matrix[$col][$row] = shift(@elements);

    }

}

my @output;

my $x = 0; # X position in matrix
my $y = 0; # Y position in matrix

my $v = 0; # Vertical direction
my $h = 1; # Horizontal direction

my $row_s = 0;     # Current Row start
my $row_e = $rows; # Current Row end
my $col_s = 0;     # Current Column start
my $col_e = $cols; # Current Column end

for my $place ( 0 .. $count-1 ) {

    #
    # Show X and Y coordinate in bounds "min<coord<max"
    # and the value at that coordinate in [ ] so we can see it work
    #
    print "$place x[$col_s<$x<$col_e] y[$row_s<$y<$row_e]",
        " [$matrix[$x][$y]]\n";

    #
    # Push the element at that matrix coordinate into the output list
    #
    $output[$place] = $matrix[$x][$y];

    if ( $h == 1 && $v == 0 && $x == $col_e && $y == $row_s ) {

        print "> reached last col. go v\n";

        $h = 0; # Stop horizontal movement (was right)
        $v = 1; # Go down

        # Finished highest remaining row
        # so remove it from matrix bounds
        $row_s++;

    }
    elsif ( $h == 0 && $v == 1 && $x == $col_e && $y == $row_e ) {

        print "v reached last row. go <\n";

        $h = -1; # Go left
        $v = 0; # Stop vertical movement (was down)

        # Finished rightmost remaining column
        # so remove it from matrix bounds
        $col_e--;

    }
    elsif ( $h == -1 && $v == 0 && $x == $col_s && $y == $row_e ) {

        print "< reached first col. go ^\n";

        $h = 0; # Stop horizontal movement (was left)
        $v = -1; # Go up

        # Finished lowest remaining row
        # so remove it from matrix bounds
        $row_e--;

    }
    elsif ( $h == 0 && $v == -1 && $x == $col_s && $y == $row_s ) {

        print "^ reached first row. go >\n";

        $h = 1; # Go right
        $v = 0; # Stop vertical movement (was up)

        # Finished leftmost remaining column
        # so remove it from matrix bounds
        $col_s++;

    }

    #
    # Increment (or decrement) matrix position pointer
    #
    $x += $h;
    $y += $v;

}

print join($/, @output), $/;

__DATA__
a b c d e f g
h i j k l m n
o p q r s t u

Try it with:

my $cols = 26;
my $rows = 26;

at the top and

__DATA__
aa ab ac ad ae af ag ah ai aj ak al am an ao ap aq ar as at au av aw a
+x ay az
ba bb bc bd be bf bg bh bi bj bk bl bm bn bo bp bq br bs bt bu bv bw b
+x by bz
ca cb cc cd ce cf cg ch ci cj ck cl cm cn co cp cq cr cs ct cu cv cw c
+x cy cz
da db dc dd de df dg dh di dj dk dl dm dn do dp dq dr ds dt du dv dw d
+x dy dz
ea eb ec ed ee ef eg eh ei ej ek el em en eo ep eq er es et eu ev ew e
+x ey ez
fa fb fc fd fe ff fg fh fi fj fk fl fm fn fo fp fq fr fs ft fu fv fw f
+x fy fz
ga gb gc gd ge gf gg gh gi gj gk gl gm gn go gp gq gr gs gt gu gv gw g
+x gy gz
ha hb hc hd he hf hg hh hi hj hk hl hm hn ho hp hq hr hs ht hu hv hw h
+x hy hz
ia ib ic id ie if ig ih ii ij ik il im in io ip iq ir is it iu iv iw i
+x iy iz
ja jb jc jd je jf jg jh ji jj jk jl jm jn jo jp jq jr js jt ju jv jw j
+x jy jz
ka kb kc kd ke kf kg kh ki kj kk kl km kn ko kp kq kr ks kt ku kv kw k
+x ky kz
la lb lc ld le lf lg lh li lj lk ll lm ln lo lp lq lr ls lt lu lv lw l
+x ly lz
ma mb mc md me mf mg mh mi mj mk ml mm mn mo mp mq mr ms mt mu mv mw m
+x my mz
na nb nc nd ne nf ng nh ni nj nk nl nm nn no np nq nr ns nt nu nv nw n
+x ny nz
oa ob oc od oe of og oh oi oj ok ol om on oo op oq or os ot ou ov ow o
+x oy oz
pa pb pc pd pe pf pg ph pi pj pk pl pm pn po pp pq pr ps pt pu pv pw p
+x py pz
qa qb qc qd qe qf qg qh qi qj qk ql qm qn qo qp qq qr qs qt qu qv qw q
+x qy qz
ra rb rc rd re rf rg rh ri rj rk rl rm rn ro rp rq rr rs rt ru rv rw r
+x ry rz
sa sb sc sd se sf sg sh si sj sk sl sm sn so sp sq sr ss st su sv sw s
+x sy sz
ta tb tc td te tf tg th ti tj tk tl tm tn to tp tq tr ts tt tu tv tw t
+x ty tz
ua ub uc ud ue uf ug uh ui uj uk ul um un uo up uq ur us ut uu uv uw u
+x uy uz
va vb vc vd ve vf vg vh vi vj vk vl vm vn vo vp vq vr vs vt vu vv vw v
+x vy vz
wa wb wc wd we wf wg wh wi wj wk wl wm wn wo wp wq wr ws wt wu wv ww w
+x wy wz
xa xb xc xd xe xf xg xh xi xj xk xl xm xn xo xp xq xr xs xt xu xv xw x
+x xy xz
ya yb yc yd ye yf yg yh yi yj yk yl ym yn yo yp yq yr ys yt yu yv yw y
+x yy yz
za zb zc zd ze zf zg zh zi zj zk zl zm zn zo zp zq zr zs zt zu zv zw z
+x zy zz

at the bottom, that way it's easier to see what it's doing because the letters correspond to columns and rows.

Also with such a large list you might want to format the output with:

my $place;
for my $row (0 .. $rows) {
    for my $col (0 .. $cols) {
        print $output[$place++], " ";
    }
    print $/;
}

instead of:

print join($/, @output), $/;