Ants on a rod walking...

output.txt

22 48
----------------------------------------------------------------
 0 -1---2---3------4----5-----
 1 1---2---3------4----5------
 2 ---2---3------4----5-------
 3 --2---3------4----5--------
 4 -2---3------4----5---------
 5 2---3------4----5----------
 6 ---3------4----5-----------
 7 --3------4----5------------
 8 -3------4----5-------------
 9 3------4----5--------------
10 ------4----5---------------
11 -----4----5----------------
12 ----4----5-----------------
13 ---4----5------------------
14 --4----5-------------------
15 -4----5--------------------
16 4----5---------------------
17 ----5----------------------
18 ---5-----------------------
19 --5------------------------
20 -5-------------------------
21 5--------------------------
22 ---------------------------
22
----------------------------------------------------------------
 0 ---1-2---3------4----5-----
 1 ----2---3------4----5------
 2 ---1-2-3------4----5-------
 3 --1---3------4----5--------
 4 -1---2-3----4----5---------
 5 1---2---3--4----5----------
 6 ---2-----34----5-----------
 7 --2-----3--4--5------------
 8 -2-----3----45-------------
 9 2-----3----4--5------------
10 -----3----4----5-----------
11 ----3----4------5----------
12 ---3----4--------5---------
13 --3----4----------5--------
14 -3----4------------5-------
15 3----4--------------5------
16 ----4----------------5-----
17 ---4------------------5----
18 --4--------------------5---
19 -4----------------------5--
20 4------------------------5-
21 --------------------------5
22 -------------------------5-
23 ------------------------5--
24 -----------------------5---
25 ----------------------5----
26 ---------------------5-----
27 --------------------5------
28 -------------------5-------
29 ------------------5--------
30 -----------------5---------
31 ----------------5----------
32 ---------------5-----------
33 --------------5------------
34 -------------5-------------
35 ------------5--------------
36 -----------5---------------
37 ----------5----------------
38 ---------5-----------------
39 --------5------------------
40 -------5-------------------
41 ------5--------------------
42 -----5---------------------
43 ----5----------------------
44 ---5-----------------------
45 --5------------------------
46 -5-------------------------
47 5--------------------------
48 ---------------------------
48

simulation.py

#!/usr/bin/env python3

MAXPOS = 27

class Ant:

    def __init__(self, index, initPos, direction=True):
        assert 0 <= initPos <= 27
        self.index = index
        self.currentPos = initPos
        self.direction = bool(direction)

    def reverse(self):
        self.direction = not self.direction

    def walk(self):
        self.currentPos += 1 if self.direction else -1
        if self.currentPos == MAXPOS: self.reverse()
        return self.currentPos

def simulate(directions=0, details=False):
    rod = [
        Ant(1, 3,  directions & (1 << 0)),
        Ant(2, 7,  directions & (1 << 1)),
        Ant(3, 11, directions & (1 << 2)),
        Ant(4, 18, directions & (1 << 3)),
        Ant(5, 23, directions & (1 << 4))
    ]
    for i in range(0, 100):
        # check for collision
        for j in range(0, len(rod) - 1):
            ant1, ant2 = rod[j], rod[j+1]
            if abs(ant1.currentPos - ant2.currentPos) <= 1 and ant1.direction != ant2.direction:
                ant1.reverse()
                ant2.reverse()
        # check for leaving ants
        leaving = [ant for ant in rod if ant.walk() <= 0]
        for leftAnt in leaving: rod.remove(leftAnt)
        # print rod status
        if details: print("%2d" % i, status(rod))
        # exit if all done
        if len(rod) < 1: return i
    raise Exception("Time too long.")

def status(rod):
    global MAXPOS
    output = ["-"] * MAXPOS
    for ant in rod:
        output[ant.currentPos-1] = str(ant.index)
    return "".join(output)

tmin, tmax = 9999999, 0
tmin_i, tmax_i = None, None
for i in range(0, 2**5):
    r = simulate(i)
    if r < tmin:
        tmin, tmin_i = r, i
    if r > tmax:
        tmax, tmax_i = r, i

print(tmin, tmax)
print("-" * 64)
print(simulate(tmin_i, True))
print("-" * 64)
print(simulate(tmax_i, True))