Populating Next Right Pointers in Each Node/ Valid Palindrome

Author: gavinfish

116 Populating Next Right Pointers in Each Node.py

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+'''
+Given a binary tree
+
+    struct TreeLinkNode {
+      TreeLinkNode *left;
+      TreeLinkNode *right;
+      TreeLinkNode *next;
+    }
+Populate each next pointer to point to its next right node. If there is no next right node, the next pointer should be set to NULL.
+
+Initially, all next pointers are set to NULL.
+
+Note:
+
+You may only use constant extra space.
+You may assume that it is a perfect binary tree (ie, all leaves are at the same level, and every parent has two children).
+For example,
+Given the following perfect binary tree,
+         1
+       /  \
+      2    3
+     / \  / \
+    4  5  6  7
+After calling your function, the tree should look like:
+         1 -> NULL
+       /  \
+      2 -> 3 -> NULL
+     / \  / \
+    4->5->6->7 -> NULL
+'''
+
+# Definition for binary tree with next pointer.
+class TreeLinkNode(object):
+    def __init__(self, x):
+        self.val = x
+        self.left = None
+        self.right = None
+        self.next = None
+
+
+class Solution(object):
+    def connect(self, root):
+        """
+        :type root: TreeLinkNode
+        :rtype: nothing
+        """
+        if not root:
+            return
+        current_level = [root]
+        while current_level:
+            next_level = []
+            for node in current_level:
+                if node.left:
+                    next_level.append(node.left)
+                if node.right:
+                    next_level.append(node.right)
+            for i in range(len(next_level) - 1):
+                next_level[i].next = next_level[i + 1]
+            current_level = next_level
+
+
+if __name__ == "__main__":
+    None

125 Valid Palindrome.py

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+'''
+Given a string, determine if it is a palindrome, considering only alphanumeric characters and ignoring cases.
+
+For example,
+"A man, a plan, a canal: Panama" is a palindrome.
+"race a car" is not a palindrome.
+
+Note:
+Have you consider that the string might be empty? This is a good question to ask during an interview.
+
+For the purpose of this problem, we define empty string as valid palindrome.
+'''
+
+class Solution(object):
+    def isPalindrome(self, s):
+        """
+        :type s: str
+        :rtype: bool
+        """
+        alphanumericS = [c for c in s.lower() if c.isalnum()]
+        return alphanumericS == alphanumericS[::-1]
+
+
+if __name__ == "__main__":
+    assert Solution().isPalindrome("A man, a plan, a canal: Panama") == True
+    assert Solution().isPalindrome("race a car") == False