370 midterm notes

370/past-midterms/2.md

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+# Time/space complexity
+
+For basically everthing, just list it out somewhere on sheet
+
+# AVL Tree's
+
+Get some functions for them written out
+Insert/Deletion/Lookup Functions
+
+# No pathfinding code
+_mainly cuz we never did any for homework/class_
+
+Time/space complexities should be straightforward memorization
+
+# Tries
+
+
+# Huffman
+
+Decoding: 
+:	Time - O(n) {n = number of input bits}
+
+Encoding
+:	Time O(nlog(n))
+:	Where n is the number of unique bits in the string
+
+
+# Pathfinding - Conceptual things
+
+Admissability: allowed to underestimate but not overestimate.
+
+> Heuristic?
+
+* A-star
+* Best-first
+
+> Multiple sources
+
+* Floyd's Algorithm
+
+> Multiple destination
+
+* Floyd's 
+* Bellman-Ford
+
+> Negative edges
+
+* Floyd
+* Bellman-Ford
+
+> Negative Cycles
+
+None

370/past-midterms/2.py

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+class HuffmanNode:
+    # $ will represent a dummy node
+    # anything  else  is a regular node
+    def __init__(self, data, freq):
+        self.data = data
+        self.freq = freq
+
+
+class HuffmanTree:
+    def __init__(self, node):
+        self.root = node
+
+    def frequencyMap(self, string):
+        ret = {}
+        for i in string:
+            if i not in ret:
+                ret[i] = Node(i, 1)
+            else:
+                ret[i].freq += 1
+
+        return ret
+
+
+    def encode(self, string):
+        f = self.frequencyMap(string)
+
+class TrieNode:
+    def __init__(self):
+        # 1 ref for each character in the alphabet
+        self.isleaf = False
+        self.edges = [0] * 26
+
+class TrieTree:
+    def __init__(self, root):
+        self.root = root
+
+    # just not going to bother with capitals
+    def _charIndex(self, char):
+        return ord(char) - ord('a')
+
+    def insert(self, string):
+        curr = self.root
+        for i in string:
+            alphabetIndex = _charIndex(i)
+            if curr[alphabetIndex] is None:
+                curr.edges[alphabetIndex] = Node()
+            # go to the nexxt thing
+            curr = curr.edges[alphabetIndex]
+        else:
+            # Finally mark the last node as a leaf
+            curr.isleaf = True
+
+    def lookup(self, string):
+        curr = self.root
+        # First we should go straight to the end of the string
+        # That's why we don't do any checks
+        for i in string:
+            alphaIndex = _charIndex(i)
+            curr = curr.edges[alphaIndex]
+
+        return curr.isleaf
+
+    def remove(self, string):
+        pass
+
+    def traverse(self, node, preFix):
+        if node:
+            if n.isleaf:
+                print(prefix)
+            # recursively go through the tree
+            for i in prefix:
+                traverse(node.edges[_i], prefix+_charIndex(i))
+
+class AVLNode:
+    def __init__(self, data):
+        self.data = data
+        self.height = 0
+        self.left = None
+        self.Right = None
+
+class AVLTree:
+    def __init__(self,node):
+        self.root = node
+    
+    def rotateLeft(self, node):
+        tmp = node.right
+        node.left = tmp.right
+        tmp.right = node
+
+        # Set the heights on each node
+        node.height = 1 + max(node.left.height, node.right.height)
+        tmp.height = 1 + max(tmp.left.height, tmp.right.height)
+        return tmp
+
+    def rotateRight(self, node):
+        pass

370/past-midterms/tmp.py

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+class Trie:
+    def __init__(self, *words):
+        self.root = {}
+
+        for word in words:
+            self.insert(word)
+
+    def insert(self, word):
+        curr = self.root
+        for c in word:
+            if c not in curr:
+                curr[c] = {}
+            else:
+                curr = curr[c]
+
+        # add a marker to show that we are a leaf
+        curr['.'] = '.'
+        self.root = curr
+
+    def remove(self, word):
+        pass
+
+    def printWord(self, word):
+        pass
+
+    def all(self):
+        pass

370/past-midterms/trie.py

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+class Node:
+    def __init__(self, leaf=False):
+        # refs list of next valid characters
+        self.letters = [None] * 26
+        self.isLeaf = leaf
+
+
+class Trie:
+    def __init__(self):
+        self.root = Node()
+
+    def _charIndex(self, char):
+        return ord(char) - ord('a')
+
+    def insert(self, string):
+        curr = self.root
+        for i in string:
+            refIndex = self._charIndex()
+            # create nodes if we have to 
+            if curr.letters[refIndex] is None:
+                curr.letters[refIndex] = Node()
+
+            curr = curr.letters[refIndex]
+        # Set the last letter to be a leaf
+        curr.isLeaf = True
+
+    def remove(self, string):
+        # Lazy removal
+        curr = self.root
+        for i in string:
+            refIndex = self._charIndex(i)
+            if curr.letters[refIndex] is None:
+                break
+            curr = curr.letters[refIndex]
+        curr.isLeaf = False
+
+
+    # We're also going to be printing things as we go along the thing
+    def lookup(self, string):
+        curr = self.root
+        for i in string:
+            refIndex = self._charIndex(i)
+            # Make sure we don't walk into nothing
+            if curr.letters[refIndex] is None:
+                return False
+            curr = curr.letters[refIndex]
+            print(i, end='')
+
+        return curr.isLeaf
+
+    def all(self, node, word):
+        if node is None:
+            return
+
+        if node.isLeaf:
+            # Print out the word we have so far
+            self.lookup(word)
+
+