lc297.java

package code;

import java.util.Arrays;
import java.util.Deque;
import java.util.LinkedList;

/*
 * 297. Serialize and Deserialize Binary Tree
 * 题意：序列化，反序列化树
 * 难度：Hard
 * 分类：Tree, Design
 * 思路：
 * Tips：lc572 序列化的应用
 */
public class lc297 {
    public class TreeNode {
        int val;
        TreeNode left;
        TreeNode right;
        TreeNode(int x) { val = x; }
    }
    public class Codec {
        private static final String spliter = ",";
        private static final String NN = "X";

        // Encodes a tree to a single string.
        public String serialize(TreeNode root) {
            StringBuilder sb = new StringBuilder();
            buildString(root, sb);
            return sb.toString();
        }

        private void buildString(TreeNode node, StringBuilder sb) {
            if (node == null) {
                sb.append(NN).append(spliter);
            } else {
                sb.append(node.val).append(spliter);
                buildString(node.left, sb);
                buildString(node.right,sb);
            }
        }
        // Decodes your encoded data to tree.
        public TreeNode deserialize(String data) {
            Deque<String> nodes = new LinkedList<>();
            nodes.addAll(Arrays.asList(data.split(spliter)));   //split
            return buildTree(nodes);
        }

        private TreeNode buildTree(Deque<String> nodes) {
            String val = nodes.remove();
            if (val.equals(NN)) return null;
            else {
                TreeNode node = new TreeNode(Integer.valueOf(val));
                node.left = buildTree(nodes);
                node.right = buildTree(nodes);
                return node;
            }
        }
    }
}