[剑指offer] 对称的二叉树

/*
public class TreeNode {
    int val = 0;
    TreeNode left = null;
    TreeNode right = null;

    public TreeNode(int val) {
        this.val = val;
    }
}
*/
public class Solution {
    boolean isSymmetrical(TreeNode pRoot)
    {
        if(pRoot == null)
            return true;
        return isSymmetrical(pRoot.left, pRoot.right);
    }
    boolean isSymmetrical(TreeNode left, TreeNode right){
        if(left == null && right == null)
            return true;
        if(left == null || right == null)
            return false;
        if(left.val == right.val){
            return isSymmetrical(left.left, right.right) && 
                isSymmetrical(left.right, right.left);
        }
        return false;
    }
}

import java.util.Stack;
public class Solution {
    boolean isSymmetrical(TreeNode pRoot)
    {
        if(pRoot == null)
            return true;
        Stack<TreeNode> s = new Stack<TreeNode>();
        s.push(pRoot.left);
        s.push(pRoot.right);
        while(!s.isEmpty()){
            TreeNode right = s.pop();
            TreeNode left = s.pop();
            if(right == null && left == null)
                continue;
            if(right == null || left == null)
                return false;
            if(right.val != left.val)
                return false;
            s.push(left.left);
            s.push(right.right);
            s.push(left.right);
            s.push(right.left);
        }
        return true;
    }
}