剑指 Offer.37-序列化二叉树

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Codec {
    // 通过层序遍历序列化
    // Encodes a tree to a single string.
    public String serialize(TreeNode root) {
        StringBuffer sb = new StringBuffer("[");
        Queue<TreeNode> queue = new LinkedList<>();  
        // 输入的合法性验证
        if(root == null) return "[]";
        queue.offer(root);
        // 当队不空时
        while(!queue.isEmpty()){
            //获取队列当前大小 进行层序遍历
            TreeNode t = queue.poll();
            if(t != null){
                sb.append(t.val + ",");
                //正常进队
                queue.offer(t.left);
                queue.offer(t.right);
            }else{
                sb.append("null,");
            }
        }
        // 删除最后一个,
        sb.deleteCharAt(sb.length()-1);
        sb.append("]");
        return sb.toString();
    }

    // Decodes your encoded data to tree.
    public TreeNode deserialize(String data) {
        if(data.equals("[]")) return null;
        // 1.去除左右两侧括号 // 2.将字符串按照,分割 转化为字符串数组
        String[] s = data.substring(1,data.length()-1).split(",");
        // 3.拿第一个节点作为根节点 层序建立
        TreeNode root = new TreeNode(Integer.parseInt(s[0]));
        Queue<TreeNode> queue = new LinkedList<>();
        queue.offer(root);
        // 遍历数组绑定左右指针
        int i = 1;
        // 再通过层序遍历构建二叉树
        while(!queue.isEmpty()){
            TreeNode element = queue.poll();
            // 判断当前绑定位置是否为null
            if(!s[i].equals("null")){
                element.left = new TreeNode(Integer.parseInt(s[i]));
                queue.offer(element.left);
            }
            i++;
            // 判断当前绑定位置是否为null
            if(!s[i].equals("null")){
                element.right = new TreeNode(Integer.parseInt(s[i]));
                queue.offer(element.right);
                
            }
            i++;
        }
        return root;
    }
}

// Your Codec object will be instantiated and called as such:
// Codec codec = new Codec();
// codec.deserialize(codec.serialize(root));