From a6a9cbccc3666ffdbf0e2a4afdb312aeddd6c024 Mon Sep 17 00:00:00 2001
From: Chau Long Do <dolong2110@gmail.com>
Date: Wed, 4 May 2022 11:42:26 +0700
Subject: [PATCH] Create stack_with_max_advanced.py

this implementation uses double linked list and it takes O(n) for all operations. It can be also used deque why deque is quietly similar to double linked list
---
 .../stack_with_max_advanced.py                | 59 +++++++++++++++++++
 1 file changed, 59 insertions(+)
 create mode 100644 2. Data Structures/Week-1-Basic Data Structures/4_stack_with_max/stack_with_max_advanced.py

diff --git a/2. Data Structures/Week-1-Basic Data Structures/4_stack_with_max/stack_with_max_advanced.py b/2. Data Structures/Week-1-Basic Data Structures/4_stack_with_max/stack_with_max_advanced.py
new file mode 100644
index 0000000..32425e0
--- /dev/null
+++ b/2. Data Structures/Week-1-Basic Data Structures/4_stack_with_max/stack_with_max_advanced.py	
@@ -0,0 +1,59 @@
+#python3
+import sys
+
+class Node:
+    def __init__(self, val, max_elem, prev=None, next=None):
+        self.val = val
+        self.max_elem = max_elem
+        self.prev = prev
+        self.next = next        
+
+class StackWithMax():
+    def __init__(self):
+        self.head = Node(-1, -1)
+        self.tail = Node(-1, -1)
+        self.head.next = self.tail
+        self.tail.prev = self.head
+        self.len = 0
+
+    def Push(self, a):
+        if not self.len:
+            node = Node(a, a, self.head, self.tail)
+            self.head.next = node
+            self.tail.prev = node
+        else:
+            prev_node = self.tail.prev
+            node = Node(a, max(a, prev_node.max_elem), prev_node, self.tail)
+            prev_node.next = node
+            self.tail.prev = node
+        self.len += 1
+
+    def Pop(self):
+        if self.len:
+            prev_node = self.tail.prev
+            prev_prev_node = prev_node.prev
+            prev_prev_node.next = self.tail
+            self.tail.prev = prev_prev_node
+            self.len -= 1
+
+    def Max(self):
+        if self.len:
+            prev_node = self.tail.prev
+            return prev_node.max_elem
+
+
+if __name__ == '__main__':
+    stack = StackWithMax()
+
+    num_queries = int(sys.stdin.readline())
+    for _ in range(num_queries):
+        query = sys.stdin.readline().split()
+        
+        if query[0] == "push":
+            stack.Push(int(query[1]))
+        elif query[0] == "pop":
+            stack.Pop()
+        elif query[0] == "max":
+            print(stack.Max())
+        else:
+            assert(0)