leetcode 100. Same Tree

Given two binary trees, write a function to check if they are the same or not.

Two binary trees are considered the same if they are structurally identical and the nodes have the same value.

Example 1:

Input:     1         1
          / \       / \
         2   3     2   3

        [1,2,3],   [1,2,3]

Output: true

Example 2:

Input:     1         1
          /           \
         2             2

        [1,2],     [1,null,2]

Output: false

Example 3:

Input:     1         1
          / \       / \
         2   1     1   2

        [1,2,1],   [1,1,2]

Output: false

# 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 isSameTree(self, p, q):
        """
        :type p: TreeNode
        :type q: TreeNode
        :rtype: bool
        """
        # DFS
        if p and q:
            return p.val == q.val and self.isSameTree(p.left, q.left) and self.isSameTree(p.right, q.right)
        else:
            return p == q

迭代解法：

public boolean isSameTree(TreeNode p, TreeNode q) {
         Stack<TreeNode> stack_p = new Stack <> ();       
         Stack<TreeNode> stack_q = new Stack <> ();
         if (p != null) stack_p.push( p ) ;
         if (q != null) stack_q.push( q ) ;
         while (!stack_p.isEmpty() && !stack_q.isEmpty()) {
             TreeNode pn = stack_p.pop() ;
             TreeNode qn = stack_q.pop() ;            
             if (pn.val != qn.val) return false ;
             if (pn.right != null) stack_p.push(pn.right) ;
             if (qn.right != null) stack_q.push(qn.right) ;
             if (stack_p.size() != stack_q.size()) return false ;
             if (pn.left != null) stack_p.push(pn.left) ;                          
             if (qn.left != null) stack_q.push(qn.left) ;
             if (stack_p.size() != stack_q.size()) return false ;
         }             
         return stack_p.size() == stack_q.size() ;     
     }