initial commit

.gitignore

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+download.py

3Sum Closest.py

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+class Solution:
+    def threeSumClosest(self, A, target):
+        A, result, closest_diff, i = sorted(A), 2147483647, 2147483647, 0
+        while i < len(A) - 2:
+            j, k = i + 1, len(A) - 1
+            while j < k:
+                diff = A[i] + A[j] + A[k] - target
+                if diff < 0:
+                    if math.fabs(diff) < math.fabs(closest_diff):
+                        result, closest_diff = A[i] + A[j] + A[k], diff
+                    j += 1
+                elif diff > 0:
+                    if math.fabs(diff) < math.fabs(closest_diff):
+                        result, closest_diff = A[i] + A[j] + A[k], diff
+                    k -= 1
+                else:
+                    return target
+            i += 1
+        return result

3Sum.py

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+class Solution:
+    def threeSum(self, A):
+        A, result, i = sorted(A), [], 0
+        while i < len(A) - 2:
+            j, k = i + 1, len(A) - 1
+            while j < k:
+                if A[i] + A[j] + A[k] < 0:
+                    j += 1
+                elif A[i] + A[j] + A[k] > 0:
+                    k -= 1
+                else:
+                    result.append([A[i], A[j], A[k]])
+                    j, k = j + 1, k - 1
+                    while j < k and A[j] == A[j - 1]:
+                        j += 1
+                    while j < k and A[k] == A[k + 1]:
+                        k -= 1
+            i += 1
+            while i < len(A) - 2 and A[i] == A[i - 1]:
+                i += 1
+        return result

Add Binary.py

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+class Solution:
+    def addBinary(self, a, b):
+        return bin(int(a, 2) + int(b, 2)).split('b')[1]

Add Two Numbers.py

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+class Solution:
+    def addTwoNumbers(self, l1, l2):
+        dummy = ListNode(0)
+        current, carry = dummy, 0
+        while l1 != None or l2 != None:
+            res = carry
+            if l1 != None:
+                res += l1.val
+                l1 = l1.next
+            if l2 != None:
+                res += l2.val
+                l2 = l2.next
+            carry, res = res / 10, res % 10
+            current.next = ListNode(res)
+            current = current.next
+        if carry == 1:
+            current.next = ListNode(1)
+        return dummy.next

Anagrams.py

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+class Solution:
+    def anagrams(self, strs):
+        map, result = {}, []
+        if len(strs) >= 1:
+            for str in strs:
+                sorted_str = "".join(sorted(str))
+                if sorted_str not in map:
+                    map[sorted_str] = [str]
+                else:
+                    map[sorted_str].append(str)
+            for word in map:
+                if len(map[word]) > 1:
+                    result += map[word]
+        return result

Balanced Binary Tree.py

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+class Solution:
+    def isBalanced(self, root):
+        return self.getHeight(root) != -1
+
+    def getHeight(self, root):
+        if root == None:
+            return 0
+        left_height, right_height = self.getHeight(root.left), self.getHeight(root.right) 
+        if left_height < 0 or right_height < 0 or math.fabs(left_height - right_height) > 1:
+            return -1
+        return max(left_height, right_height) + 1

Best Time to Buy and Sell Stock II.py

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+class Solution:
+    def maxProfit(self, prices):
+        profit = 0
+        for i in range(len(prices) - 1):
+            if (prices[i] < prices[i+1]):
+                profit += prices[i+1] - prices[i]
+        return profit

Best Time to Buy and Sell Stock III.py

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+class Solution:
+    def maxProfit(self, prices):
+        min_price, max_profit = 9223372036854775807, 0
+        profits_before = [0 for i in range(len(prices))]
+        for i in range(len(prices)):
+            min_price = min(prices[i], min_price)
+            max_profit = max(prices[i] - min_price, max_profit)
+            profits_before[i] = max_profit
+        max_price, max_profit = -9223372036854775808, 0
+        profits_after = [0 for i in range(len(prices))]
+        for i in reversed(range(len(prices))):
+            max_price = max(prices[i], max_price)
+            max_profit = max(max_price - prices[i], max_profit)
+            profits_after[i] = max_profit
+        return reduce(lambda acc, i: max(profits_before[i] + profits_after[i], acc), range(len(prices)), 0)

Best Time to Buy and Sell Stock.py

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+class Solution:
+    def maxProfit(self, prices):
+        min_price = 9223372036854775807
+        max_profit = 0
+        for i in range(len(prices)):
+            min_price = min(prices[i], min_price)
+            max_profit = max(prices[i] - min_price, max_profit)
+        return max_profit

Binary Tree Inorder Traversal.py

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+class Solution:
+    def inorderTraversal(self, root):
+        result = []
+        self.recur(root, result)
+        return result
+
+    def recur(self, root, result):
+        if(root == None):
+            return
+        self.recur(root.left, result)
+        result.append(root.val)
+        self.recur(root.right, result)

Binary Tree Level Order Traversal II.py

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+class Solution:
+    def levelOrderBottom(self, root):
+        result = []
+        if root == None:
+            return result
+        current = [root]
+        while len(current) > 0:
+            # Python is just so slow, but who I can complain? I have to write following code to optimize for skewed tree 
+            # -- None of the code from this tag to the next tag is actually needed -- #
+            if len(current) == 1 and (current[0].left == None or current[0].right== None):
+                this_node = current[0]
+                result.insert(0, [this_node.val])
+                if this_node.left == None and this_node.right != None:
+                    current = [this_node.right]
+                elif this_node.left != None and this_node.right == None:
+                    current = [this_node.left]
+                else:
+                    current.pop(0)
+            else:
+            # -- None of the code above this tag up to the previous tag is actually needed -- #
+                vals = []
+                size = len(current)
+                for i in range(size):
+                    this_node = current[0]
+                    vals.append(this_node.val)
+                    if i < len(current) - 1:
+                        this_node.next = current[i+1]
+                    if this_node.left != None:
+                        current.append(this_node.left)
+                    if this_node.right != None:
+                        current.append(this_node.right)
+                    current.pop(0)
+                result.insert(0, vals)
+        return result

Binary Tree Level Order Traversal.py

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+class Solution:
+    def levelOrder(self, root):
+        result = []
+        if root == None:
+            return result
+        current = [root]
+        while len(current) > 0:
+            # Python is just so slow, but who I can complain? I have to write following code to optimize for skewed tree 
+            # -- None of the code from this tag to the next tag is actually needed -- #
+            if len(current) == 1 and (current[0].left == None or current[0].right== None):
+                this_node = current[0]
+                result.append([this_node.val])
+                if this_node.left == None and this_node.right != None:
+                    current = [this_node.right]
+                elif this_node.left != None and this_node.right == None:
+                    current = [this_node.left]
+                else:
+                    current.pop(0)
+            else:
+            # -- None of the code above this tag up to the previous tag is actually needed -- #
+                vals = []
+                size = len(current)
+                for i in range(size):
+                    this_node = current[0]
+                    vals.append(this_node.val)
+                    if i < len(current) - 1:
+                        this_node.next = current[i+1]
+                    if this_node.left != None:
+                        current.append(this_node.left)
+                    if this_node.right != None:
+                        current.append(this_node.right)
+                    current.pop(0)
+                result.append(vals)
+        return result

Binary Tree Postorder Traversal.py

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+class Solution:
+    def postorderTraversal(self, root):
+        result = []
+        self.recur(root, result)
+        return result
+
+    def recur(self, root, result):
+        if(root == None):
+            return
+        self.recur(root.left, result)
+        self.recur(root.right, result)
+        result.append(root.val)

Binary Tree Preorder Traversal.py

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+class Solution:
+    def preorderTraversal(self, root):
+        result = []
+        self.recur(root, result)
+        return result
+
+    def recur(self, root, result):
+        if(root == None):
+            return
+        result.append(root.val)
+        self.recur(root.left, result)
+        self.recur(root.right, result)

Binary Tree Zigzag Level Order Traversal.py

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+class Solution:
+    def zigzagLevelOrder(self, root):
+        result = []
+        if root == None:
+            return result
+        current, reverse = [root], 0
+        while len(current) > 0:
+            # Python is just so slow, but who I can complain? I have to write following code to optimize for skewed tree 
+            # -- None of the code from this tag to the next tag is actually needed -- #
+            if len(current) == 1 and (current[0].left == None or current[0].right== None):
+                this_node = current[0]
+                result.append([this_node.val])
+                if this_node.left == None and this_node.right != None:
+                    current = [this_node.right]
+                elif this_node.left != None and this_node.right == None:
+                    current = [this_node.left]
+                else:
+                    current.pop(0)
+            else:
+            # -- None of the code above this tag up to the previous tag is actually needed -- #
+                vals = []
+                size = len(current)
+                for i in range(size):
+                    this_node = current[0]
+                    if reverse:
+                        vals.insert(0, this_node.val)
+                    else:
+                        vals.append(this_node.val)
+                    if i < len(current) - 1:
+                        this_node.next = current[i+1]
+                    if this_node.left != None:
+                        current.append(this_node.left)
+                    if this_node.right != None:
+                        current.append(this_node.right)
+                    current.pop(0)
+                result.append(vals)
+                reverse = 1 - reverse
+        return result

Candy.py

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+class Solution:
+    def candy(self, ratings):
+        candies = [1 for i in range(len(ratings))]
+        for i in range(1, len(ratings)):
+            if ratings[i] > ratings[i - 1]:
+                candies[i] = candies[i - 1] + 1
+        for i in reversed(range(1, len(ratings))):
+            if ratings[i - 1] > ratings[i] and candies[i - 1] <= candies[i]:
+                candies[i - 1] = candies[i] + 1
+        return reduce(operator.add, candies)

Climbing Stairs.py

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+class Solution:
+    def climbStairs(self, n):
+        prev, current = 1, 0
+        for i in range(n + 1):
+            prev, current = current, prev + current
+        return current

Combination Sum II.py

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+class Solution:
+    def combinationSum2(self, candidates, target):
+        result = []
+        self.combinationSumRecur(sorted(candidates), result, [], 0, target)
+        return result
+
+    def combinationSumRecur(self, candidates, result, current, start, target):
+        if target == 0 and current not in result:
+            result.append(current)
+        else:
+            while start < len(candidates) and candidates[start] <= target:
+                self.combinationSumRecur(candidates, result, current + [candidates[start]], start + 1, target - candidates[start])
+                start += 1

Combination Sum.py

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+class Solution:
+    def combinationSum(self, candidates, target):
+        result = []
+        self.combinationSumRecur(sorted(candidates), result, [], 0, target)
+        return result
+
+    def combinationSumRecur(self, candidates, result, current, start, target):
+        if target == 0:
+            result.append(current)
+        else:
+            while start < len(candidates) and candidates[start] <= target:
+                self.combinationSumRecur(candidates, result, current + [candidates[start]], start, target - candidates[start])
+                start += 1

Combinations.py

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+class Solution:
+    def combine(self, n, k):
+        return self.combineRecur([], n, k, 1)
+
+    def combineRecur(self, current, n, k, i):
+        if k == 0:
+            return [current]
+        if i > n:
+            return []
+        return self.combineRecur(current, n, k, i + 1) + self.combineRecur(current + [i], n, k - 1, i + 1)

Construct Binary Tree from Inorder and Postorder Traversal.py

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+class Solution:
+    def buildTree(self, inorder, postorder):
+        # using dictionary for index lookup improves the performance of algorithm from O(N^2) to O(N), where N = |postorder|
+        lookup = {}
+        for i in range(len(inorder)):
+            lookup[inorder[i]] = i 
+        return self.buildTreeRecur(lookup, inorder, postorder, 0, len(postorder) - 1, len(postorder) - 1)
+
+    def buildTreeRecur(self, lookup, inorder, postorder, in_start, in_end, post_end):
+        if in_start > in_end:
+            return None
+        current = TreeNode(postorder[post_end])
+        i = lookup[postorder[post_end]]
+        current.left = self.buildTreeRecur(lookup, inorder, postorder, in_start, i - 1, post_end - (in_end - i) - 1)
+        current.right = self.buildTreeRecur(lookup, inorder, postorder, i + 1, in_end, post_end - 1)
+        return current

Construct Binary Tree from Preorder and Inorder Traversal.py

@@ -0,0 +1,16 @@
+class Solution:
+    def buildTree(self, preorder, inorder):
+        # using dictionary for index lookup improves the performance of algorithm from O(N^2) to O(N), where N = |preorder|
+        lookup = {}
+        for i in range(len(inorder)):
+            lookup[inorder[i]] = i 
+        return self.buildTreeRecur(lookup, preorder, inorder, 0, len(preorder) - 1, 0)
+
+    def buildTreeRecur(self, lookup, preorder, inorder, in_start, in_end, pre_start):
+        if in_start > in_end:
+            return None
+        current = TreeNode(preorder[pre_start])
+        i = lookup[preorder[pre_start]]
+        current.left = self.buildTreeRecur(lookup, preorder, inorder, in_start, i - 1, pre_start + 1)
+        current.right = self.buildTreeRecur(lookup, preorder, inorder, i + 1, in_end, pre_start + i - in_start + 1)
+        return current