Added solution to ch3-5 and associated tests.

Author: diadical

src/chapter3/ch3-q5.js

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+'use strict';
+
+function peek(stack) {
+  return stack[stack.length - 1];
+}
+
+function isEmpty(stack) {
+  return stack.length === 0;
+}
+
+/**
+ * Sort the stack by taking one item off the input stack at a time, find the
+ * right place within the processed items in the temp stack to insert it into.
+ * Insertion is done by holding the next value aside and moving the temp stack
+ * values into the input stack until the right spot is found.
+ *
+ * N = |stack|
+ * Time: O(N^2)
+ * Additional space: O(1) - while there are 2 stacks there are only a fixed
+ * number of items.
+ */
+export function sortStack(stack) {
+  let temp = [];
+  temp.push(stack.pop());
+  while (!isEmpty(stack)) {
+    let curr = stack.pop(),
+      count = 0;
+
+    while (!isEmpty(temp) && curr < peek(temp)) {
+      stack.push(temp.pop());
+      ++count;
+    }
+    temp.push(curr);
+    for (let i = 0; i < count; ++i) {
+      temp.push(stack.pop());
+    }
+  }
+
+  while (!isEmpty(temp)) {
+    stack.push(temp.pop());
+  }
+
+  return stack;
+}

src/chapter3/ch3-q5.spec.js

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+import { expect } from 'chai';
+import * as funcs from './ch3-q5';
+
+for (let key in funcs) {
+  let func = funcs[key];
+
+  describe('ch3-q5: ' + key, function() {
+
+    it('does not crash on an empty list', function() {
+      let stack = [];
+      expect(() => func(stack)).to.not.throw(Error).and.to.equal(stack);
+    });
+
+    it('works with a single element stack', function() {
+      expect(func([4])).to.eql([4]);
+    });
+
+    [
+      [5, 3, 1, 4, 6, 2],
+      [9, 8, 7, 6, 5, 4, 3, 2, 1],
+      [1, 2, 1, 2, 1, 2, 1, 2],
+      [1, 2, 3, 4, 5, 6, 7, 8, 9],
+      [100, 15, 20, 30, 10, 80, 50, 45, 75, 35, 85, 55, 40, 99]
+    ].forEach(arg => {
+
+      it(`correctly sorts ${arg}`, function() {
+        let expected = arg.slice(0).sort((a, b) => a < b ? 1 : a > b ? -1 : 0);
+
+        expect(func(arg)).to.eql(expected);
+      });
+
+    });
+
+    it('correctly sorts with 100 random numbers', function() {
+      let stack = [];
+      for (let i = 0; i < 100; ++i) {
+        stack.push(Math.trunc(Math.random() * 9999999));
+      }
+      let expected = stack.slice(0).sort((a, b) => a < b ? 1 : a > b ? -1 : 0);
+      expect(func(stack)).to.eql(expected);
+    });
+
+  });
+}