Feat | NeetCode | Roadmap | #22 Min Stack

README.md

@@ -93,4 +93,5 @@
   - [Task #19](src/neetcode/sliding-window/minimum-window-substring) – _Minimum Window Substring_ - _[check the task](https://neetcode.io/problems/minimum-window-with-characters)_
   - [Task #20](src/neetcode/sliding-window/sliding-window-maximum) – _Sliding Window Maximum_ - _[check the task](https://neetcode.io/problems/sliding-window-maximum)_
 - Stack
-  - [Task #21](src/neetcode/stack/valid-parentheses) – _Valid Parentheses_ - _[check the task](https://leetcode.com/problems/valid-parentheses)_
+  - [Task #21](src/neetcode/stack/valid-parentheses) – _Valid Parentheses_ - _[check the task](https://leetcode.com/problems/valid-parentheses)_
+  - [Task #22](src/neetcode/stack/min-stack) – _Min Stack_ - _[check the task](https://leetcode.com/problems/minimum-stack)_

src/neetcode/stack/min-stack/solution.test.ts

@@ -0,0 +1,69 @@
+import { MinStack } from './solution';
+
+describe('Min Stack | NeetCode | RoadMap | Testcases', () => {
+  test('#1 Keeps the minimum after pop', () => {
+    const stack = new MinStack();
+
+    stack.push(1);
+    stack.push(2);
+    stack.push(0);
+
+    expect(stack.getMin()).toBe(0);
+
+    stack.pop();
+
+    expect(stack.top()).toBe(2);
+    expect(stack.getMin()).toBe(1);
+  });
+
+  test('#2 Supports negative numbers', () => {
+    const stack = new MinStack();
+
+    stack.push(-2);
+    stack.push(0);
+    stack.push(-3);
+
+    expect(stack.getMin()).toBe(-3);
+
+    stack.pop();
+
+    expect(stack.top()).toBe(0);
+    expect(stack.getMin()).toBe(-2);
+  });
+
+  test('#3 Keeps duplicate minimum values', () => {
+    const stack = new MinStack();
+
+    stack.push(2);
+    stack.push(1);
+    stack.push(1);
+    stack.push(3);
+
+    expect(stack.getMin()).toBe(1);
+
+    stack.pop();
+    stack.pop();
+
+    expect(stack.top()).toBe(1);
+    expect(stack.getMin()).toBe(1);
+
+    stack.pop();
+
+    expect(stack.top()).toBe(2);
+    expect(stack.getMin()).toBe(2);
+  });
+
+  test('#4 Handles push after pop', () => {
+    const stack = new MinStack();
+
+    stack.push(10);
+    stack.pop();
+    stack.push(20);
+
+    expect(stack.top()).toBe(20);
+
+    stack.push(-20);
+
+    expect(stack.getMin()).toBe(-20);
+  });
+});

src/neetcode/stack/min-stack/solution.ts

@@ -0,0 +1,42 @@
+export class MinStack {
+  curMin = Infinity;
+  minStack: number[] = [];
+  stack: number[] = [];
+
+  /**
+   * Pushes the element `val` onto the stack.
+   * @param {number} val
+   * @return {void}
+   */
+  push(val: number): void {
+    this.curMin = Math.min(this.curMin, val);
+    this.minStack.push(this.curMin);
+    this.stack.push(val);
+  }
+
+  /**
+   *  Removes the element on the top of the stack.
+   * @return {void}
+   */
+  pop(): void {
+    this.stack.pop();
+    this.minStack.pop();
+    this.curMin = this.minStack[this.minStack.length - 1] ?? Infinity;
+  }
+
+  /**
+   * gets the top element of the stack.
+   * @return {number}
+   */
+  top(): number {
+    return this.stack[this.stack.length - 1];
+  }
+
+  /**
+   * retrieves the minimum element in the stack.
+   * @return {number}
+   */
+  getMin(): number {
+    return this.curMin;
+  }
+}