Copy List With Random Pointer

0138.Copy-List-with-Random-Pointer/memo.md

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+# 138. Copy List with Random Pointer
+
+## step1
+
+頭から実装するとstep1.pyとなった。
+
+同じ処理が現れたので関数化したが、getattrなどが何度も現れてわかりづらい
+
+## step2
+
+ソリューションを漁る
+
+https://leetcode.com/problems/copy-list-with-random-pointer/solutions/379056/python-solution-with-comments-on-using-a-xf3k/?envType=problem-list-v2&envId=7p5x763
+
+再帰を使うのは思いつかなかった
+```python
+def copyRandomList(self, head: 'Optional[Node]', seen={None: None}) -> 'Optional[Node]':
+    """ O(N)TS """
+    if head not in seen:
+        seen[head] = Node(head.val)
+        seen[head].next = self.copyRandomList(head.next, seen)
+        seen[head].random = self.copyRandomList(head.random, seen)
+    return seen[head]
+```
+
+https://leetcode.com/problems/copy-list-with-random-pointer/solutions/7052593/on-and-o1-solutions-by-russelldcosta-lbh8/?envType=problem-list-v2&envId=7p5x763
+
+Hashmapを使わずに解ける。空間計算量がO(1)になる。

0138.Copy-List-with-Random-Pointer/step1.py

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+"""
+# Definition for a Node.
+"""
+
+
+class Node:
+    def __init__(self, x: int, next: "Node" = None, random: "Node" = None):
+        self.val = int(x)
+        self.next = next
+        self.random = random
+
+
+class Solution:
+    def copyRandomList(self, head: Node | None) -> Node | None:
+        if head is None:
+            return head
+        copy_head = Node(x=head.val)
+        original_to_copy = {head: copy_head}
+        node = head
+        node_copy = copy_head
+        while node is not None:
+            if node.next is not None:
+                if node.next in original_to_copy:
+                    node_copy.next = original_to_copy[node.next]
+                else:
+                    node_copy.next = Node(x=node.next.val)
+                    original_to_copy[node.next] = node_copy.next
+            if node.random is not None:
+                if node.random in original_to_copy:
+                    node_copy.random = original_to_copy[node.random]
+                else:
+                    node_copy.random = Node(x=node.random.val)
+                    original_to_copy[node.random] = node_copy.random
+            node = node.next
+            node_copy = node_copy.next
+        return copy_head

0138.Copy-List-with-Random-Pointer/step1_revised.py

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+"""
+# Definition for a Node.
+"""
+
+
+class Node:
+    def __init__(self, x: int, next: "Node" = None, random: "Node" = None):
+        self.val = int(x)
+        self.next = next
+        self.random = random
+
+
+class Solution:
+    def copyRandomList(self, head: Node | None) -> Node | None:
+        if head is None:
+            return head
+
+        copy_head = Node(x=head.val)
+        original_to_copy = {head: copy_head}
+        node = head
+        node_copy = copy_head
+
+        def update_attribute(node: Node, node_copy: Node, attribute: str) -> None:
+            nonlocal original_to_copy
+            if getattr(node, attribute) in original_to_copy:
+                setattr(
+                    node_copy, attribute, original_to_copy[getattr(node, attribute)]
+                )
+            else:
+                setattr(node_copy, attribute, Node(x=getattr(node, attribute).val))
+                original_to_copy[getattr(node, attribute)] = getattr(
+                    node_copy, attribute
+                )
+
+        while node is not None:
+            if node.next is not None:
+                update_attribute(node, node_copy, "next")
+            if node.random is not None:
+                update_attribute(node, node_copy, "random")
+            node = node.next
+            node_copy = node_copy.next
+        return copy_head

0138.Copy-List-with-Random-Pointer/step2_wo_hashmap.py

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+class Node:
+    def __init__(self, x: int, next: "Node" = None, random: "Node" = None):
+        self.val = int(x)
+        self.next = next
+        self.random = random
+
+
+class Solution:
+    def copyRandomList(self, head: "Node" | None) -> "Node" | None:
+        if head is None:
+            return None
+
+        # original1->copy1->original2->copy2...
+        node = head
+        while node:
+            node_next = node.next
+            copy_node = Node(x=node.val)
+            node.next = copy_node
+            copy_node.next = node_next
+            node = node_next
+
+        # コピーしたノードのrandomを繋ぐ
+        node = head
+        while node:
+            if node.random:
+                node.next.random = node.random.next
+            node = node.next.next
+
+        # コピーを分離する
+        node = head
+        dummy_head = Node(0)
+        copy_node = dummy_head
+
+        while node:
+            node_next = node.next.next
+
+            copy_node_next = node.next
+            copy_node.next = copy_node_next
+            copy_node = copy_node_next
+
+            node.next = node_next
+            node = node_next
+
+        return dummy_head.next

0138.Copy-List-with-Random-Pointer/step3_wo_hashmap.py

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+from __future__ import annotations
+
+
+class Node:
+    def __init__(self, x: int, next: Node = None, random: Node = None):
+        self.val = int(x)
+        self.next = next
+        self.random = random
+
+
+class Solution:
+    def copyRandomList(self, head: Node | None) -> Node | None:
+        if head is None:
+            return None
+
+        node = head
+        while node:
+            node_next = node.next
+            copy_node = Node(x=node.val)
+            node.next = copy_node
+            copy_node.next = node_next
+            node = node_next
+
+        node = head
+        while node:
+            if node.random:
+                node.next.random = node.random.next
+            node = node.next.next
+
+        node = head
+        dummy_head = Node(0)
+        copy_node = dummy_head
+
+        while node:
+            node_next = node.next.next
+
+            copy_node_next = node.next
+            copy_node.next = copy_node_next
+            copy_node = copy_node_next
+
+            node.next = node_next
+            node = node_next
+
+        return dummy_head.next