二叉树的序列化与反序列化

解题思路

序列化时，直接使用广度遍历，不用多讲。主要把null也一并保存
反序列化时，同样可以使用队列和广度遍历，每次将节点的左子树和右子树赋值。同时将左子树和右子树进队列。

代码

java

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Codec {

    // Encodes a tree to a single string.
    public String serialize(TreeNode root) {
        if(root==null){
            return "";
        }
        Queue<TreeNode> que = new LinkedList<TreeNode> ();
        que.offer(root);
        String res = "";
        while(!que.isEmpty()){      // 只要队列不空，一直循环，意味着还没有遍历结束
            TreeNode t = que.poll();
            if(t==null){
                res += "null,";
                continue;
            }
            if(t.left != null){
                que.offer(t.left);      // 进入队列，这样可以保证先进先出
            }else{
                que.offer(null);
            }
            if(t.right!= null){
                que.offer(t.right);
            }else{
                que.offer(null);
            }
            res += String.valueOf(t.val)+",";
        }
        return res;
    }

    // Decodes your encoded data to tree.
    public TreeNode deserialize(String data) {
        if(data==null || data.length()==0){
            return null;
        }
        String []s = data.split(",");
        int i = 0;
        TreeNode t = new TreeNode(Integer.valueOf(s[i++]));
        Queue<TreeNode> que = new LinkedList<TreeNode>();
        que.offer(t);
        while(!que.isEmpty()){
            TreeNode n = que.poll();
            if(!s[i].equals("null")){
                n.left =new TreeNode(Integer.valueOf(s[i++]));
                que.offer(n.left);
            }else{
                i++;
            }
            if(!s[i].equals ("null")){
                n.right =new TreeNode(Integer.valueOf(s[i++]));
                que.offer(n.right);
            }else{
                i++;
            }
            
        }
        
        return t;
    }
}

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