Add solution #155

Author: JoshCrozier

README.md

@@ -149,6 +149,7 @@
 149|[Max Points on a Line](./0149-max-points-on-a-line.js)|Hard|
 151|[Reverse Words in a String](./0151-reverse-words-in-a-string.js)|Medium|
 152|[Maximum Product Subarray](./0152-maximum-product-subarray.js)|Medium|
+155|[Min Stack](./0155-min-stack.js)|Medium|
 160|[Intersection of Two Linked Lists](./0160-intersection-of-two-linked-lists.js)|Medium|
 162|[Find Peak Element](./0162-find-peak-element.js)|Medium|
 164|[Maximum Gap](./0164-maximum-gap.js)|Medium|

solutions/0155-min-stack.js

@@ -0,0 +1,50 @@
+/**
+ * 155. Min Stack
+ * https://leetcode.com/problems/min-stack/
+ * Difficulty: Medium
+ *
+ * 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.
+ */
+
+
+var MinStack = function() {
+  this.stack = [];
+};
+
+/**
+ * @param {number} val
+ * @return {void}
+ */
+MinStack.prototype.push = function(val) {
+  this.stack.push({ val, min: this.stack.length ? Math.min(val, this.getMin()) : val });
+};
+
+/**
+ * @return {void}
+ */
+MinStack.prototype.pop = function() {
+  this.stack.pop();
+};
+
+/**
+ * @return {number}
+ */
+MinStack.prototype.top = function() {
+  return this.stack[this.stack.length - 1].val;
+};
+
+/**
+ * @return {number}
+ */
+MinStack.prototype.getMin = function() {
+  return this.stack.length ? this.stack[this.stack.length - 1].min : 0;
+};