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Polish find loop start solution.

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Donne Martin 2016-02-20 12:53:27 -05:00
parent 7a166bed67
commit 9c441e9f18
1 changed files with 28 additions and 34 deletions
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62
linked_lists/find_loop_start/find_loop_start_solution.ipynb
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@ -60,12 +60,12 @@
"source": [ "source": [
"## Algorithm\n", "## Algorithm\n",
"\n", "\n",
"* Use two pointers i, j, initialized to the head\n", "* Use two references `slow`, `fast`, initialized to the `head`\n",
"* Increment i and j until they meet\n", "* Increment `slow` and `fast` until they meet\n",
" * j is incremented twice as fast as i\n", " * `fast` is incremented twice as fast as `slow`\n",
" * If j's next is None, we do not have a circular list\n", " * If `fast.next` is `None`, we do not have a circular list\n",
"* When i and j meet, move j to the head\n", "* When `slow` and `fast` meet, move `slow` to the `head`\n",
"* Increment i and j one node at a time until they meet\n", "* Increment `slow` and `fast` one node at a time until they meet\n",
"* Where they meet is the start of the loop\n", "* Where they meet is the start of the loop\n",
"\n", "\n",
"Complexity:\n", "Complexity:\n",
@ -103,29 +103,23 @@
"\n", "\n",
" def find_loop_start(self):\n", " def find_loop_start(self):\n",
" if self.head is None or self.head.next is None:\n", " if self.head is None or self.head.next is None:\n",
" return\n", " return None\n",
" i = self.head\n", " slow = self.head\n",
" j = self.head\n", " fast = self.head\n",
" i = i.next\n", " while fast.next is not None:\n",
" j = j.next.next\n", " slow = slow.next\n",
"\n", " fast = fast.next.next\n",
" # Increment i and j until they meet\n", " if fast is None:\n",
" # j is incremented twice as fast as i\n", " return None\n",
" while j != i:\n", " if slow.data == fast.data:\n",
" i = i.next\n", " break\n",
" if j is None or j.next is None:\n", " slow = self.head\n",
" return\n", " while slow.data != fast.data:\n",
" j = j.next.next\n", " slow = slow.next\n",
"\n", " fast = fast.next\n",
" # When i and j meet, move j to the head\n", " if fast is None:\n",
" j = self.head\n", " return None\n",
"\n", " return slow.data"
" # Increment i and j one node at a time until\n",
" # they meet, which is the start of the loop\n",
" while j != i:\n",
" i = i.next\n",
" j = j.next\n",
" return i.data"
] ]
}, },
{ {
@ -230,21 +224,21 @@
], ],
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