From 3a5f0b5eeb9d362d5f2966ef9e73117d977d1196 Mon Sep 17 00:00:00 2001
From: praxpk <23168694+praxpk@users.noreply.github.com>
Date: Tue, 23 Dec 2025 19:10:02 -0500
Subject: [PATCH] min stack and hash set

---
 hash_set.py  | 67 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 min_stack.py | 36 ++++++++++++++++++++++++++++
 2 files changed, 103 insertions(+)
 create mode 100644 hash_set.py
 create mode 100644 min_stack.py

diff --git a/hash_set.py b/hash_set.py
new file mode 100644
index 00000000..4c5722a5
--- /dev/null
+++ b/hash_set.py
@@ -0,0 +1,67 @@
+"""
+// Time Complexity :
+    add - o(n)
+    remove - o(n)
+    contains - 0(n)
+// Space Complexity : o(n)
+// Did this code successfully run on Leetcode : yes
+// Any problem you faced while coding this : yes, made an error in contains but managed to correct the error
+"""
+
+
+class Node:
+    def __init__(self, val, nxt=None, prev=None):
+        self.val = val
+        self.next = nxt
+        self.prev = prev
+
+
+class MyHashSet:
+
+    def __init__(self):
+        self.prime_mod = 997
+        self.set_list = [None] * self.prime_mod
+
+    def add(self, key: int) -> None:
+        index = key % self.prime_mod
+        val_node = Node(key)
+        if ptr := self.set_list[index]:
+            while ptr:
+                if ptr.val == key:
+                    return
+                if not ptr.next:
+                    ptr.next = val_node
+                    val_node.prev = ptr
+                    return
+                ptr = ptr.next
+        else:
+            dummy = Node(None)
+            dummy.next = val_node
+            val_node.prev = dummy
+            self.set_list[index] = dummy
+
+    def remove(self, key: int) -> None:
+        index = key % self.prime_mod
+        if head := self.set_list[index]:
+            ptr = head.next
+            while ptr:
+                if ptr.val == key:
+                    prev = ptr.prev
+                    nxt = ptr.next
+                    prev.next = nxt
+                    if nxt:
+                        nxt.prev = prev
+                    if prev == head and not head.next:
+                        self.set_list[index] = None
+                    return
+                ptr = ptr.next
+
+    def contains(self, key: int) -> bool:
+        index = key % self.prime_mod
+        if head := self.set_list[index]:
+            ptr = head.next
+            while ptr:
+                if ptr.val == key:
+                    return True
+                ptr = ptr.next
+        return False
diff --git a/min_stack.py b/min_stack.py
new file mode 100644
index 00000000..d50c16d1
--- /dev/null
+++ b/min_stack.py
@@ -0,0 +1,36 @@
+"""
+// Time Complexity :
+    push - o(1)
+    pop - o(1)
+    top - 0(1)
+    get_min - o(1)
+// Space Complexity : o(n)
+// Did this code successfully run on Leetcode : yes
+// Any problem you faced while coding this : yes, knew I had to use two stacks but had doubts with my approach, had to look at editorial to
+confirm my approach was right
+"""
+
+
+class MinStack:
+
+    def __init__(self):
+        self.stack = []
+        self.mins = []
+
+    def push(self, val: int) -> None:
+        self.stack.append(val)
+        if not self.mins:
+            self.mins.append(val)
+        elif self.mins[-1] >= val:
+            self.mins.append(val)
+
+    def pop(self) -> None:
+        element = self.stack.pop()
+        if self.mins[-1] == element:
+            self.mins.pop()
+
+    def top(self) -> int:
+        return self.stack[-1]
+
+    def getMin(self) -> int:
+        return self.mins[-1]