From 6d5e78822a4f7bdd2ad99a67685cbf11627b5787 Mon Sep 17 00:00:00 2001
From: Michael Stanton <mvstanton@mvstanton-macbookpro.roam.corp.google.com>
Date: Sat, 5 Sep 2015 11:19:15 +0200
Subject: [PATCH] Added interview questions.

---
 interviewqs/parsetree.js | 112 +++++++++++++++++++++++++++++++++++++++
 kynumbers/kynumbers.js   |   2 +-
 2 files changed, 113 insertions(+), 1 deletion(-)
 create mode 100644 interviewqs/parsetree.js

diff --git a/interviewqs/parsetree.js b/interviewqs/parsetree.js
new file mode 100644
index 0000000..ad51717
--- /dev/null
+++ b/interviewqs/parsetree.js
@@ -0,0 +1,112 @@
+// parsetree.js
+// represent expressions like "3 + 6 * 8" and evaluate them.
+// Also operate on the expression tree to derive new expressions.
+
+function print(str) {
+  console.log(str);
+}
+
+var TOKEN = {
+  INVALID:   { value: 0, name: "INVALID" },
+  OPERATOR:  { value: 1, name: "operator" },
+  NUMBER:    { value: 2, name: "number" },
+  SYMBOL:    { value: 3, name: "symbol" }
+};
+
+var OPERATOR = {
+  PLUS:       { value: 0, name: "+", binding: 0 },
+  MINUS:      { value: 1, name: "-", binding: 0 },
+  TIMES:      { value: 2, name: "*", binding: 1 },
+  DIVIDE:     { value: 3, name: "/", binding: 1 },
+  POWER:      { value: 4, name: "^", binding: 1 }
+};
+
+function Expr(token, data, left, right) {
+  this.left = left;
+  this.right = right;
+  this.token = token;
+  this.data = data;
+}
+
+
+function number(data) {
+  return new Expr(TOKEN.NUMBER, data);
+}
+
+function operator(op, left, right) {
+  return new Expr(TOKEN.OPERATOR, op, left, right);
+}
+
+// printer should have a method append(str).
+Expr.prototype.print = function(printer) {
+  var expr = this;
+
+  if (expr.token == TOKEN.OPERATOR) {
+    expr.left.print(printer);
+    printer.append(" ");
+    printer.append(expr.data.name);
+    printer.append(" ");
+    // Should there be paranthesis around the right expression?
+    var use_paren = false;
+    if (expr.right.token == TOKEN.OPERATOR) {
+      if (expr.right.data.binding < expr.data.binding) {
+        use_paren = true;
+      }
+    }
+    if (use_paren) printer.append("(");
+    expr.right.print(printer);
+    if (use_paren) printer.append(")");
+  } else if (expr.token == TOKEN.NUMBER) {
+    printer.append(expr.data.toString());
+  } else if (expr.token == TOKEN.SYMBOL) {
+    printer.append(expr.data);
+  }
+
+  return printer;
+}
+
+
+function example_one() {
+  var expr = operator(OPERATOR.PLUS,
+                      number(3),
+                      operator(OPERATOR.TIMES,
+                               number(6),
+                               number(8)));
+  return expr;
+}
+
+function example_two() {
+  return operator(OPERATOR.TIMES,
+                  number(6),
+                  operator(OPERATOR.PLUS,
+                           number(3),
+                           operator(OPERATOR.PLUS,
+                                    number(16),
+                                    number(8))));
+}
+
+function Printer() {
+  this.buffer = "";
+}
+
+Printer.prototype.append = function(str) {
+  this.buffer += str;
+}
+
+Printer.prototype.flush = function() {
+  print(this.buffer);
+  this.buffer = "";
+}
+
+function main() {
+  var printer = new Printer();
+  number(5).print(printer).flush();
+  operator(OPERATOR.PLUS, number(5), number(5)).print(printer).flush();
+  var expr = example_one();
+  expr.print(printer).flush();
+
+  expr = example_two();
+  expr.print(printer).flush();
+}
+
+main();
diff --git a/kynumbers/kynumbers.js b/kynumbers/kynumbers.js
index 6757cca..65687e6 100644
--- a/kynumbers/kynumbers.js
+++ b/kynumbers/kynumbers.js
@@ -46,7 +46,7 @@ var KYNumbers = (function() {
     // Compute soul number.
     var soulNumber = reduceNumber(day);
     result.push(new Pair(FEATURE.SOUL, soulNumber));
-
+    
     // Compute karma number.
     var karmaNumber = reduceNumber(month);
     result.push(new Pair(FEATURE.KARMA, karmaNumber));