判断两个二叉树是否相等

题目：判断两个二叉树是否相等

思路：递归与迭代

递归:

public static boolean isSameRec(TreeNode root1,TreeNode root2){
        if(root1 == null && root2 == null){
            return true;
        }else if(root1 == null || root2 == null){
            return false;
        }else if(root1.val != root2.val){
            return false;
        }
        
        boolean left = isSameRec(root1.left,root2.left);
        boolean right = isSameRec(root1.right,root2.right);
        return left&right;
    }

迭代：迭代要注意，借助了两个辅助栈，要注意的是，若某一节点的左孩子或右孩子为null，也要添加到栈中。

public static boolean isSameTree(TreeNode root1,TreeNode root2){
        if(root1 == null && root2 == null){
            return true;
        }else if(root1 == null || root2 == null){
            return false;
        }else if(root1.val != root2.val){
            return false;
        }
        
        Stack<TreeNode> stack1 = new Stack<TreeNode>();
        Stack<TreeNode> stack2 = new Stack<TreeNode>();
        stack1.push(root1);
        stack2.push(root2);
        
        while(!stack1.isEmpty() && !stack2.isEmpty()){
            TreeNode n1 = stack1.pop();
            TreeNode n2 = stack2.pop();
            if(n1 == null && n2 == null){
                continue;
            }
            else if(n1 != null && n2 != null && n1.val == n2.val){
                stack1.push(n1.left);
                stack1.push(n1.right);
                stack2.push(n2.left);
                stack2.push(n2.right);
            }else {
                return false;
            }
        }
        
        return true;
    }