third commit

Leetcode/May-Day-01-2022-Backspace-String.py

@@ -26,6 +26,7 @@
 
 
 class Solution:
+    # Time - Space = O(n),O(n)
     def backspaceCompare(self, s: str, t: str) -> bool:
         def build(s):
             ans = []
@@ -37,6 +38,7 @@ def build(s):
             return "".join(ans)
         return build(s) == build(t)
 
+    # Time - Space = O(n),O(1)
     def backspaceCompare1(self,s:str,t:str) -> bool:
         def getNextChar(string,pointer):
             num_of_backspaces = 0

Topic-Wise/Binary_Search_Tree/reconstrutBST.py

@@ -0,0 +1,55 @@
+# Given preorder traversal of a binary search tree, construct the BST.
+
+# For example, if the given traversal is {10, 5, 1, 7, 40, 50}, then the output should be the root of the following tree.
+
+#      10
+#    /   \
+#   5     40
+#  /  \      \
+# 1    7      50
+
+# This is an input class. Do not edit.
+class BST:
+    def __init__(self, value, left=None, right=None):
+        self.value = value
+        self.left = left
+        self.right = right
+
+
+def reconstructBst(preOrderTraversalValues):
+    # Write your code here.
+	n = len(preOrderTraversalValues)
+	if n == 0:
+		return None 
+	rightIdx = n
+	for i in range(1,n):
+		if preOrderTraversalValues[0] <= preOrderTraversalValues[i]:
+			rightIdx = i
+			break
+	leftpotv = reconstructBst(preOrderTraversalValues[1:rightIdx])
+	rightpotv = reconstructBst(preOrderTraversalValues[rightIdx:])
+	return BST(preOrderTraversalValues[0],leftpotv,rightpotv)
+
+
+
+
+class TreeInfo:
+	def __init__(self,rootIdx):
+		self.rootIdx = rootIdx
+
+def reconstructBst1(preOrderTraversalValues):
+    # Write your code here.
+	treeInfo = TreeInfo(0)
+	return reconstructBstRange(float("-inf"),float("inf"),preOrderTraversalValues,treeInfo)
+
+def reconstructBstRange(lowerBound,upperBound,preOrderTraversalValues,currentSubtreeInfo):
+	if currentSubtreeInfo.rootIdx == len(preOrderTraversalValues):
+		return None
+
+	rootValue = preOrderTraversalValues[currentSubtreeInfo.rootIdx]
+	if rootValue < lowerBound or rootValue >= upperBound:
+		return None
+	currentSubtreeInfo.rootIdx += 1
+	leftSubtree = reconstructBstRange(lowerBound,rootValue,preOrderTraversalValues,currentSubtreeInfo)
+	rightSubtree = reconstructBstRange(rootValue,upperBound,preOrderTraversalValues,currentSubtreeInfo)
+	return BST(rootValue,leftSubtree,rightSubtree)

Topic-Wise/Binary_Search_Tree/validateBST.py

@@ -0,0 +1,20 @@
+# Definition for a binary tree node.
+# class TreeNode:
+#     def __init__(self, val=0, left=None, right=None):
+#         self.val = val
+#         self.left = left
+#         self.right = right
+class Solution:
+    def isValidBST(self, root: Optional[TreeNode]) -> bool:
+        return self.isValidBSTHelper(root,float("-inf"),float("inf"))
+
+    def isValidBSTHelper(self,root,minValue,maxValue):
+        if root == None:
+            return True
+        if root.left != None and root.val <= root.left.val:
+            return False
+        if root.right != None and root.val >= root.right.val:
+            return False
+        if root.val <= minValue or root.val >= maxValue:
+            return False
+        return self.isValidBSTHelper(root.left,minValue,root.val) and self.isValidBSTHelper(root.right,root.val,maxValue)