{
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  {
   "cell_type": "markdown",
   "id": "d33ba928",
   "metadata": {},
   "source": [
    "# 19-17 · Dlaczego ciało porusza się od ogona\n",
    "\n",
    "Praktyka do sekcji [„Dlaczego ciało porusza się od ogona”](/pl/chapters/rozdzial-19/19-17-pochemu-s-hvosta.html)."
   ]
  },
  {
   "cell_type": "markdown",
   "id": "be3df9fe",
   "metadata": {},
   "source": [
    "## Cel\n",
    "\n",
    "By pokazać, że ulepszenie z ogon-głowa nie traci na znaczeniu."
   ]
  },
  {
   "cell_type": "markdown",
   "id": "97e5867b",
   "metadata": {},
   "source": [
    "## Sprawa robocza"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
   "id": "72bb5945",
   "metadata": {
    "execution": {
     "iopub.execute_input": "2026-09-03T00:53:57.472114Z",
     "iopub.status.busy": "2026-09-03T00:53:57.471944Z",
     "iopub.status.idle": "2026-09-03T00:53:57.507483Z",
     "shell.execute_reply": "2026-09-03T00:53:57.506901Z"
    }
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "[(20, 0), (0, 0), (-20, 0)]\n"
     ]
    }
   ],
   "source": [
    "def move_from_tail(segments, head_pos):\n",
    "    segments = list(segments)\n",
    "    for i in range(len(segments) - 1, 0, -1):\n",
    "        segments[i] = segments[i - 1]\n",
    "    if segments:\n",
    "        segments[0] = head_pos\n",
    "    return segments\n",
    "\n",
    "print(move_from_tail([(0, 0), (-20, 0), (-40, 0)], (20, 0)))"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "646b89ed",
   "metadata": {},
   "source": [
    "## Zadanie ★★ Znajdź błąd w odwrotnej kolejności"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "id": "b0e4c9ab",
   "metadata": {
    "execution": {
     "iopub.execute_input": "2026-09-03T00:53:57.508996Z",
     "iopub.status.busy": "2026-09-03T00:53:57.508820Z",
     "iopub.status.idle": "2026-09-03T00:53:57.514547Z",
     "shell.execute_reply": "2026-09-03T00:53:57.513958Z"
    }
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Правильно: [(20, 0), (0, 0), (-20, 0)]\n",
      "Сломано: [(20, 0), (20, 0), (20, 0)]\n",
      "Подтверждено: обратный порядок схлопывает сегменты в одну точку.\n"
     ]
    }
   ],
   "source": [
    "def move_from_head_BROKEN(segments, head_pos):\n",
    "    segments = list(segments)\n",
    "    segments[0] = head_pos\n",
    "    for i in range(1, len(segments)):\n",
    "        segments[i] = segments[i - 1]   # уже перезаписанное значение!\n",
    "    return segments\n",
    "\n",
    "correct = move_from_tail([(0, 0), (-20, 0), (-40, 0)], (20, 0))\n",
    "broken = move_from_head_BROKEN([(0, 0), (-20, 0), (-40, 0)], (20, 0))\n",
    "print(\"Правильно:\", correct)\n",
    "print(\"Сломано:\", broken)\n",
    "assert correct == [(20, 0), (0, 0), (-20, 0)]\n",
    "assert broken == [(20, 0), (20, 0), (20, 0)]   # все сегменты схлопнулись\n",
    "print(\"Подтверждено: обратный порядок схлопывает сегменты в одну точку.\")"
   ]
  }
 ],
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