Added reverse linked and valid parentheses

Author: nhistory

reverse-linked-list/nhistory.js

@@ -0,0 +1,63 @@
+/**
+ * Definition for singly-linked list.
+ * function ListNode(val, next) {
+ *     this.val = (val===undefined ? 0 : val)
+ *     this.next = (next===undefined ? null : next)
+ * }
+ */
+/**
+ * @param {ListNode} head
+ * @return {ListNode}
+ */
+
+// Declare linked list
+function ListNode(val) {
+  this.val = val;
+  this.next = null;
+}
+
+var reverseList = function (head) {
+  let prev = null;
+  let curr = head;
+  let next;
+
+  while (curr !== null) {
+    next = curr.next;
+    curr.next = prev;
+    prev = curr;
+    curr = next;
+  }
+  return prev;
+};
+
+// Create liked list nodes
+const node1 = new ListNode(1);
+const node2 = new ListNode(2);
+const node3 = new ListNode(3);
+const node4 = new ListNode(4);
+const node5 = new ListNode(5);
+
+node1.next = node2;
+node2.next = node3;
+node3.next = node4;
+node4.next = node5;
+
+// Print out linked list
+let current = node1;
+while (current !== null) {
+  console.log(current.val);
+  current = current.next;
+}
+
+// Reversed linked list
+const reversedHead = reverseList(node1);
+
+// Print out reversed linked list
+current = reversedHead;
+while (current !== null) {
+  console.log(current.val);
+  current = current.next;
+}
+
+// TC: O(n)
+// SC: O(1)

valid-parentheses/nhistory.js

@@ -0,0 +1,26 @@
+/**
+ * @param {string} s
+ * @return {boolean}
+ */
+var isValid = function (s) {
+  // Create stack array
+  let stack = [];
+  // Iterate string to find there is an open bracket
+  for (char of s) {
+    // If it is an open bracket, push the close bracket into stack array
+    if (char === "(") stack.push(")");
+    else if (char === "{") stack.push("}");
+    else if (char === "[") stack.push("]");
+    // If it is not an open bracket, compare last element of stack array
+    else if (char !== stack.pop()) return false;
+  }
+  // Check stack array still has any element after iteration
+  return stack.length === 0;
+};
+
+// TC: O(n)
+// MC: O(n)
+
+console.log(isValid("()")); //true
+console.log(isValid("()[]{}")); //true
+console.log(isValid("([)]")); //false