Categorize scripts

utilities/python/binary_search.py

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+def binary_search(arr, target):
+    left = 0;
+    right = len(arr) - 1
+    while left < right:
+        mid = left + (right - left) / 2;
+        if arr[mid] == target:
+            return mid
+        elif arr[mid] < target:
+            left = mid + 1
+        else:
+            right = mid - 1
+    return left
+
+print(binary_search([1, 2, 3, 10], 1) == 0)
+print(binary_search([1, 2, 3, 10], 2) == 1)
+print(binary_search([1, 2, 3, 10], 3) == 2)
+print(binary_search([1, 2, 3, 10], 10) == 3)
+print(binary_search([1, 2, 3, 10], 9) == 3)
+print(binary_search([1, 2, 3, 10], 4) == 3)
+print(binary_search([1, 2, 3, 10], 0) == 0)
+print(binary_search([1, 2, 3, 10], 11) == 3)
+print(binary_search([5, 7, 8, 10], 3) == 0)

utilities/python/char_prime_map.py

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+# For mapping a lowercase character to a prime number.
+# Useful for checking whether two strings are anagram or permutations of each other.
+primes = {
+    'a': 2, 'b': 3, 'c': 5, 'd': 7, 'e': 11, 'f': 13,
+    'g': 17, 'h': 19, 'i': 23, 'j': 29, 'k': 31, 'l': 37,
+    'm': 41, 'n': 43, 'o': 47, 'p': 53, 'q': 59, 'r': 61,
+    's': 67, 't': 71, 'u': 73, 'v': 79, 'w': 83, 'x': 89,
+    'y': 97, 'z': 101, ' ': 103,
+}
+
+import functools
+
+def mul(seq):
+    return functools.reduce(lambda a, b: a * b, seq, 1)
+
+def prime_value_of_string(string):
+    return mul([primes[c] for c in string])
+
+print(prime_value_of_string('abcde'))

utilities/python/graph_dfs.py

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+def graph_dfs(matrix):
+    rows, cols = len(matrix), len(matrix[0])
+    visited = set()
+    directions = ((0, 1), (0, -1), (1, 0), (-1, 0))
+    def dfs(i, j):
+        if (i, j) in visited:
+            return
+        visited.add((i, j))
+        # Traverse neighbors.
+        for direction in directions:
+            next_i, next_j = i + direction[0], j + direction[1]
+            if 0 <= next_i < rows and 0 <= next_j < cols: # Check boundary.
+                # Add any other checking here ^
+                dfs(next_i, next_j)
+
+    for i in range(rows):
+        for j in range(cols):
+            dfs(i, j)
+
+graph_dfs([
+    [1, 2, 3, 4],
+    [5, 6, 7, 8],
+    [9, 10, 11, 12],
+])

utilities/python/graph_dijkstra.py

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+# TODO

utilities/python/graph_topo_sort.py

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+def graph_topo_sort(num_nodes, edges):
+    from collections import deque
+    nodes, order, queue = {}, [], deque()
+    for node_id in range(num_nodes):
+        nodes[node_id] = { 'in': 0, 'out': set() }
+    for node_id, pre_id in edges:
+        nodes[node_id]['in'] += 1
+        nodes[pre_id]['out'].add(node_id)
+    for node_id in nodes.keys():
+        if nodes[node_id]['in'] == 0:
+            queue.append(node_id)
+    while len(queue):
+        node_id = queue.pop()
+        for outgoing_id in nodes[node_id]['out']:
+            nodes[outgoing_id]['in'] -= 1
+            if nodes[outgoing_id]['in'] == 0:
+                queue.append(outgoing_id)
+        order.append(node_id)
+    return order if len(order) == num_nodes else []
+
+print(graph_topo_sort(3, [[0, 1], [0, 2]]))

utilities/python/is_subsequence.py

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+def is_subsequence(s, t):
+    """
+    :type s: str
+    :type t: str
+    :rtype: bool
+    """
+    if len(s) > len(t):
+        return False
+    matched_s = 0
+    for char in t:
+        if matched_s < len(s) and s[matched_s] == char:
+            matched_s += 1
+    return matched_s == len(s)

utilities/python/string_rabin_karp.py

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+# TODO

utilities/python/tree_equal.py

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+def tree_equal(node1, node2):
+    if not node1 and not node2:
+        return True
+    if not node1 or not node2:
+        return False
+    return node1.val == node2.val and \
+        tree_equal(node1.left, node2.left) and \
+        tree_equal(node1.right, node2.right)

utilities/python/tree_mirror.py

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+def tree_mirror(node):
+    if not node:
+        return
+    node.left, node.right = node.right, node.left
+    tree_mirror(node.left)
+    tree_mirror(node.right)

utilities/python/tree_traversal.py

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+# Various iterative ways of traversing a tree.
+def inorder_traversal(root):
+    """
+    :type root: TreeNode
+    :rtype: List[int]
+    """
+    if not root:
+      return []
+    result = []
+    stack = [root]
+    while len(stack) > 0:
+        curr_node = stack.pop()
+        if curr_node.left:
+            stack.append(curr_node)
+            stack.append(curr_node.left)
+            curr_node.left = None
+        else:
+            result.append(curr_node.val)
+            if curr_node.right:
+                stack.append(curr_node.right)
+    return result
+
+def preorder_traversal(root):
+    """
+    :type root: TreeNode
+    :rtype: List[int]
+    """
+    if not root:
+        return []
+    result = []
+    stack = [root]
+    while len(stack) > 0:
+        curr_node = stack.pop()
+        result.append(curr_node.val)
+        if curr_node.right:
+            stack.append(curr_node.right)
+        if curr_node.left:
+            stack.append(curr_node.left)
+    return result
+
+def postorder_traversal(root):
+    """
+    :type root: TreeNode
+    :rtype: List[int]
+    """
+    if not root:
+        return []
+    result = []
+    stack = [root]
+    while len(stack) > 0:
+        curr_node = stack.pop()
+        if curr_node.left:
+            stack.append(curr_node)
+            stack.append(curr_node.left)
+            curr_node.left = None
+        elif curr_node.right:
+            stack.append(curr_node)
+            stack.append(curr_node.right)
+            curr_node.right = None
+        else:
+            result.append(curr_node.val)
+    return result

utilities/python/trie.py

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+class Trie(object):
+    def __init__(self):
+        """
+        Initialize your data structure here.
+        """
+        self.d = {}
+
+    def insert(self, word):
+        """
+        Inserts a word into the trie.
+        :type word: str
+        :rtype: void
+        """
+        curr = self.d
+        for char in word:
+            if char not in curr:
+                curr[char] = {}
+            curr = curr[char]
+        curr['#'] = {} # Using an empty dict rather than a boolean value makes recursive traversal easier.
+
+    def search(self, word):
+        """
+        Returns if the word is in the trie.
+        :type word: str
+        :rtype: bool
+        """
+        curr = self.d
+        for char in word:
+            if char in curr:
+                curr = curr[char]
+            else:
+                return False
+        return '#' in curr
+
+    def startsWith(self, prefix):
+        """
+        Returns if there is any word in the trie that starts with the given prefix.
+        :type prefix: str
+        :rtype: bool
+        """
+        curr = self.d
+        for char in prefix:
+            if char in curr:
+                curr = curr[char]
+            else:
+                return False
+        return True
+
+    def searchRegex(self, word):
+        """
+        Returns if the word is in the data structure. A word could contain the dot character '.' to represent any one letter.
+        :type word: str
+        :rtype: bool
+        """
+        def traverse(node, index):
+            if len(word) == index:
+                return '#' in node
+            char = word[index]
+            if char == '.':
+                for key in node.keys():
+                    if traverse(node[key], index+1):
+                        return True
+                return False
+            else:
+                if char not in node:
+                    return False
+                return traverse(node[char], index + 1)
+        return traverse(self.d, 0)
+
+# Example
+trie = Trie()
+trie.insert('hello')
+print(trie.search('hello') == True)
+print(trie.startsWith('hello') == True)
+print(trie.startsWith('hel') == True)
+print(trie.search('world') == False)
+print(trie.startsWith('wor') == False)
+print(trie.searchRegex('..llo') == True)
+print(trie.searchRegex('..llx') == False)
+print(trie.searchRegex('..') == False)