序列化二叉树

序列化二叉树：
层次遍历的改进，定义一个数值sum用来存储当前队列中不为空值的个数。

public static String Serialize(TreeNode root) {
        String result = "";
        if(root == null) {
            result = "null";
            return result;
        }
        StringBuffer str = new StringBuffer();
        Queue<TreeNode> queue = new LinkedList<>();
        queue.add(root);
        int sum = 1; //用来记录队列中当前不为空的个数
        while(sum!=0){
            TreeNode t = queue.poll();
            if(t == null ){
                str.append("null");
            }else{
                if(t.left!=null) {
                    sum++;
                }
                if(t.right!=null) {
                    sum++;
                }
                queue.add(t.left);
                queue.add(t.right);
                str.appe***al);
                sum--;
            }
            if(sum > 0) 
                str.append(",");
        }
        result = str.toString();
        return result;
    }

反序列化二叉树
定义一个数组treeNodes用来存放val值等于序列中的值TreeNode节点。

TreeNode Deserialize(String str) {
    TreeNode head = null;    
    if(str == null || str.length() == 0)        
        return head;     
    String[] nodes = str.split(",");   
    TreeNode[] treeNodes = new TreeNode[nodes.length];    
    for(int i=0; i<nodes.length; i++){       
    if(!nodes[i].equals("null"))          
        treeNodes[i] = new TreeNode(Integer.valueOf(nodes[i]));   
    }      
    for(int i=0, j=1; j<treeNodes.length; i++){        
        if(treeNodes[i] != null){        
            treeNodes[i].left = treeNodes[j++];
            if(j<treeNodes.length)
                 treeNodes[i].right = treeNodes[j++];      
        }     
    }   
return treeNodes[0];
}