[Leetcode]101. Symmetric Tree

# Definition for a binary tree node.
# class TreeNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution(object):
    def check_sym(self, nodes):
        if len(nodes) <= 1:
            return True 
        
        head = 0 
        tail = len(nodes)-1
        while(head < tail):
            if nodes[head] == None and nodes[tail]  == None:
                head += 1
                tail -= 1 
            elif nodes[head] != None and nodes[tail]  == None or nodes[head] == None and nodes[tail]  != None:
                return False            
            elif nodes[head].val != nodes[tail].val:
                return False 
            else:
                head += 1
                tail -= 1
                
        return True 
	
    def next_level_nodes(self, nodes):
        next_level = [] 
        while nodes:
            node = nodes.pop() 
            if node != None:
                next_level = [node.left , node.right] + next_level

return next_level
    
        
    
    
    def isSymmetric(self, root):
        """
        :type root: TreeNode
        :rtype: bool
        """
        if root == None:
            return True 
        else:
            nodes_same_level = [root] 
            
            while len(nodes_same_level)> 0:
                if self.check_sym(nodes_same_level):
                    nodes_same_level = self.next_level_nodes(nodes_same_level)                   
                else:
                    return False
                
            return True

# recursively         
    
    def isMirror(self, left, right):
        if left == None and right == None:
            return True
        elif left == None or right == None:
            return False
        else:
            if left.val == right.val:
                return self.isMirror(left.left ,right.right) and self.isMirror(left.right , right,left)
            else:
                return False 
    
            
    def isSymmetric2(self, root):
		if root == None:
            return True 
        else:
            return self.isMirror(root.left ,root.right)

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