From c6e0d0c63b2cab667f815a5c85f5399548058381 Mon Sep 17 00:00:00 2001
From: Matt <matt.smith@digital.gov.au>
Date: Mon, 9 Jul 2018 17:53:56 +1000
Subject: [PATCH] now with collision handling

---
 python/app/hash_table.py        | 25 +++++++++++++++++++++++--
 python/tests/test_hash_table.py | 19 +++++++++++++++++++
 2 files changed, 42 insertions(+), 2 deletions(-)

diff --git a/python/app/hash_table.py b/python/app/hash_table.py
index b3956a0..c9675e0 100644
--- a/python/app/hash_table.py
+++ b/python/app/hash_table.py
@@ -5,10 +5,31 @@ def __init__(self, size=100):
         self.values = self.size * [None]
 
     def get(self, x):
-        return self.values[self.h(x)]
+        if not x:
+            raise ValueError('Invalid key')
+
+        i = self.h(x)
+        result = None
+
+        if self.values[i]:
+            pair = [p[1] for p in self.values[i] if p[0] == x]
+            if pair:
+                result = pair[0]
+
+        return result
 
     def set(self, x, y):
-        self.values[self.h(x)] = y
+        """Uses separate chaining for collsions
+        """
+        if not x:
+            raise ValueError('Invalid key')
+
+        i = self.h(x)
+
+        if not self.values[i]:
+            self.values[i] = []
+
+        self.values[i].append([x, y])
 
     def h(self, x):
         return hash(x) % self.size
diff --git a/python/tests/test_hash_table.py b/python/tests/test_hash_table.py
index 724e19c..aaaf453 100644
--- a/python/tests/test_hash_table.py
+++ b/python/tests/test_hash_table.py
@@ -1,3 +1,4 @@
+import pytest
 from app.hash_table import HashTable
 
 
@@ -6,3 +7,21 @@ def test_get_set():
     ht.set('test', 1)
     assert ht.get('test') == 1
     assert ht.get('invalid') is None
+
+
+def test_invalid_key():
+    ht = HashTable()
+    with pytest.raises(ValueError):
+        ht.set(None, 1)
+
+    with pytest.raises(ValueError):
+        ht.get(None)
+
+
+def test_collisions():
+    ht = HashTable(1)
+    ht.set('test', 1)
+    ht.set('test2', 2)
+    assert ht.get('test') == 1
+    assert ht.get('test2') == 2
+    assert ht.get('test3') is None