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Author: wuduhren

problems/design-add-and-search-words-data-structure.py

@@ -0,0 +1,35 @@
+class Node(object):
+    def __init__(self, char):
+        self.char = char
+        self.children = {}
+        
+class WordDictionary(object):
+
+    def __init__(self):
+        self.root = Node('')
+        self.endSign = ';'
+
+    def addWord(self, word):
+        word = word + self.endSign
+        node = self.root
+        for c in word:
+            if c not in node.children:
+                node.children[c] = Node(c)
+            node = node.children[c]
+        
+    def search(self, word):
+        word = word + self.endSign
+        return self.searchFromNode(self.root, word)
+    
+    def searchFromNode(self, node, word):
+        if not word: return True
+        
+        char = word[0]
+        if char in node.children:
+            return self.searchFromNode(node.children[char], word[1:])
+        elif char=='.':
+            for c in node.children:
+                if self.searchFromNode(node.children[c], word[1:]):
+                    return True
+        return False
+        

problems/implement-trie-prefix-tree.py

@@ -0,0 +1,46 @@
+"""
+Time for insert() O(N), search() O(N), startsWith() O(N). N is the number of characters.
+Space for insert() O(N), search() O(1), startsWith() O(1). N is the number of characters.
+
+Use . to represent the end of a string.
+"""
+class Node(object):
+    def __init__(self, char):
+        self.char = char
+        self.children = {}
+
+class Trie(object):
+
+    def __init__(self):
+        self.period = '.'
+        self.root = Node('')
+        
+
+    def insert(self, word):
+        word = word + self.period
+        node = self.root
+        
+        for c in word:
+            if c not in node.children:
+                node.children[c] = Node(c)
+            node = node.children[c]
+        
+
+    def search(self, word):
+        word = word + self.period
+        node = self.root
+        
+        for c in word:
+            if c not in node.children:
+                return False
+            node = node.children[c]
+        return True
+        
+
+    def startsWith(self, prefix):
+        node = self.root
+        for c in prefix:
+            if c not in node.children:
+                return False
+            node = node.children[c]
+        return True

problems/range-sum-query-mutable.py

@@ -0,0 +1,67 @@
+"""
+Time: O(LogN) for all operations.
+Space: O(N) for the segment tree.
+
+Build a segment tree from the array `nums`. Each node store the info of the segment in nums (from `node.start` to `node.end`)
+And `node.val` is equal to sum from nums[start] to nums[end]
+"""
+class NumArray(object):
+
+    def __init__(self, nums):
+        def buildSegmentTree(start, end):
+            if start>end: return None
+            node = Node(start, end)
+            
+            if start==end:
+                node.val = nums[end]
+            else:
+                node.left = buildSegmentTree(start, node.mid)
+                node.right = buildSegmentTree(node.mid+1, end)
+                node.val = (node.left.val if node.left else 0) + (node.right.val if node.right else 0)
+            
+            return node
+        
+        self.root = buildSegmentTree(0, len(nums)-1)
+        
+        
+    def update(self, i, val):
+        def helper(node, i, val):
+            if node.start==node.end==i:
+                node.val = val
+                return
+            
+            if node.mid<i:
+                helper(node.right, i, val)
+            elif i<=node.mid:
+                helper(node.left, i, val)
+            node.val = (node.left.val if node.left else 0) + (node.right.val if node.right else 0)
+            
+        return helper(self.root, i, val)
+                
+        
+
+    def sumRange(self, i, j):
+        def helper(node, i, j):
+            if not node: return 0
+            if node.start==i and node.end==j:
+                return node.val
+            elif node.mid<i:
+                return helper(node.right, i, j)
+            elif j<=node.mid:
+                return helper(node.left, i, j)
+            else:
+                return helper(node.left, i, node.mid)+helper(node.right, node.mid+1, j)
+        return helper(self.root, i, j)
+        
+
+
+class Node(object):
+    def __init__(self, start, end):
+        self.start = start
+        self.end = end
+        self.mid = (start+end)/2
+        self.val = 0
+        
+        self.left = None
+        self.right = None
+