{
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   "metadata": {},
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   "source": [
    "def ternarySearch(target, nums, left, right):\n",
    "\n",
    "  if left > right:\n",
    "    return -1\n",
    "\n",
    "  mid1 = left  + (right-left+1) // 3\n",
    "  mid2 = right - (right-left+1) // 3\n",
    "\n",
    "  if nums[mid1] == target:\n",
    "    return mid1\n",
    "\n",
    "  if nums[mid2] == target:\n",
    "    return mid2\n",
    "\n",
    "  if target > nums[mid1]:\n",
    "    # target must be on the left segment\n",
    "    return ternarySearch(target,nums,left,mid1-1)\n",
    "\n",
    "  if target < nums[mid1] and target > nums[mid2]:\n",
    "    # target must be on the middle segment\n",
    "    return ternarySearch(target,nums,mid1+1,mid2-1)\n",
    "\n",
    "  # target must be on the right segment\n",
    "  return ternarySearch(target,nums,mid2+1,right)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "6\n",
      "-1\n",
      "54\n",
      "-1\n"
     ]
    }
   ],
   "source": [
    "def main():\n",
    "  nums = [443,339,333,231,202,17,11,9,8,7,6,5,4,1]\n",
    "  for target in [11,111]:\n",
    "    print(ternarySearch(target,nums,0,len(nums)-1))  # should print 6 and -1\n",
    "\n",
    "  nums = [10*i for i in range(100,0,-1)]\n",
    "  for target in [460,466]:\n",
    "    print(ternarySearch(target,nums,0,len(nums)-1))  # should print 54 and -1\n",
    "\n",
    "main()"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 10,
   "metadata": {},
   "outputs": [],
   "source": [
    "def ternarySearch(target, nums, left, right):\n",
    "\n",
    "  if left > right:\n",
    "    return -1\n",
    "  \n",
    "  if nums[left  + (right-left+1) // 3] == target:\n",
    "    return left  + (right-left+1) // 3\n",
    "\n",
    "  if nums[right - (right-left+1) // 3] == target:\n",
    "    return right - (right-left+1) // 3\n",
    "\n",
    "  if target > nums[left  + (right-left+1) // 3]:\n",
    "    # target must be on the left segment\n",
    "    return ternarySearch(target,nums,left,left  + (right-left+1) // 3 - 1)\n",
    "\n",
    "  if target < nums[left  + (right-left+1) // 3] and target > nums[right - (right-left+1) // 3]:\n",
    "    # target must be on the middle segment\n",
    "    return ternarySearch(target,nums,left  + (right-left+1) // 3 + 1,right - (right-left+1) // 3-1)\n",
    "\n",
    "  # target must be on the right segment\n",
    "  return ternarySearch(target,nums,right - (right-left+1) // 3+1,right)"
   ]
  }
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