Write LeetCode Post " LeetCode : 155. Min Stack "

_posts/2024-02-25-LeetCode-Min-Stack.md

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+---
+layout: post
+title: " LeetCode : 155. Min Stack "
+categories: LeetCode
+author: goodGid
+use_math: true
+---
+* content
+{:toc}
+
+## Min Stack
+
+### Problem
+
+```
+Design a stack that supports push, pop, top, and retrieving the minimum element in constant time.
+
+Implement the MinStack class:
+
+MinStack() initializes the stack object.
+void push(int val) pushes the element val onto the stack.
+void pop() removes the element on the top of the stack.
+int top() gets the top element of the stack.
+int getMin() retrieves the minimum element in the stack.
+You must implement a solution with O(1) time complexity for each function.
+```
+
+
+---
+
+### Example
+
+```
+["MinStack","push","push","push","getMin","pop","top","getMin"]
+[[],[-2],[0],[-3],[],[],[],[]]
+```
+
+---
+
+### [1] Code (24. 02. 25)
+
+*Retry*
+
+``` java
+// Runtime: 4 ms
+// Memory Usage: 44.8 MB
+// Ref : https://leetcode.com/submissions/detail/1184496240
+class MinStack {
+    private int size;
+    private List<Node> list;
+
+    public MinStack() {
+        size = 0;
+        list = new ArrayList<>();
+    }
+
+    public void push(int val) {
+        int prevMin = val;
+        if (size > 0) {
+            prevMin = list.get(size - 1).min;
+        }
+        list.add(new Node(val, Math.min(prevMin, val)));
+        size++;
+    }
+
+    public void pop() {
+        list.remove(size - 1);
+        size--;
+    }
+
+    public int top() {
+        return list.get(size - 1).val;
+    }
+
+    public int getMin() {
+        return list.get(size - 1).min;
+    }
+}
+
+class Node {
+    int val;
+    int min;
+
+    public Node(int _val, int _min) {
+        this.val = _val;
+        this.min = _min;
+    }
+}
+```
+
+* 처음에 [코드](https://leetcode.com/submissions/detail/1184495209)를 제출했는데 실수가 발생했다.
+
+``` java
+public void push(int val) {
+    int prevMin = val + 1; // [1]
+    if (size > 0) {
+        prevMin = list.get(size - 1).min;
+    }
+    list.add(new Node(val, Math.min(prevMin, val)));
+    size++;
+}
+```
+
+* [1] : prevMin+1을 하면서 Max.Integer 값이 들어오면 Overflow가 발생했다.
+
+  그래서 해당 부분을 "int prevMin = val;" 이렇게 수정해줘서 제출해서 패스했다.
+
+---
+
+> Review
+
+* 굉장히 재밌었던 문제였다.
+
+---
+
+## Reference
+
+* [155. Min Stack](https://leetcode.com/problems/min-stack)