[数据结构与算法]剑指 Offer 37. 序列化二叉树（层次遍历）

[剑指 Offer 37. 序列化二叉树](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 {

    // Encodes a tree to a single string.
    public String serialize(TreeNode root) {
        List<String> list = new ArrayList<>();
        Deque<TreeNode> q = new LinkedList<>();
        q.offer(root);
        while(!q.isEmpty()) {
            TreeNode node = q.poll();
            if(node == null) {
                list.add(" ");
                continue;
            } else {
                list.add("" + node.val);
            }
            q.offer(node.left);
            q.offer(node.right);
        }
        StringBuilder sb = new StringBuilder();
        for(int i = 0; i < list.size(); i++) {
            if(i > 0) {
                sb.append(",");
            }
            sb.append(list.get(i));
        }
        return sb.toString();
    }

    // Decodes your encoded data to tree.
    public TreeNode deserialize(String data) {
        int pos = 0;
        String[] split = data.split(",");
        if(split.length == 0 || " ".equals(split[0])) return null;
        TreeNode root = new TreeNode(Integer.parseInt(split[pos++]));
        Deque<TreeNode> q = new ArrayDeque<>();
        q.offer(root);
        while(q.size() > 0) {
            int size = q.size();
            int len = size;
            List<TreeNode> list = new ArrayList<>();
            List<String> valList = new ArrayList<>();
            while(size-- > 0) {
                list.add(q.poll());
                valList.add(split[pos++]);
                valList.add(split[pos++]);
            }
            for(int i = 0; i < len; i++) {
                TreeNode node = list.get(i);
                String leftS = valList.get(i * 2);
                String rightS = valList.get(i * 2 + 1);
                node.left = node.right = null;
                if(!" ".equals(leftS)) {
                    node.left = new TreeNode(Integer.parseInt(leftS));
                    q.offer(node.left);
                }
                if(!" ".equals(rightS)) {
                    node.right = new TreeNode(Integer.parseInt(rightS));
                    q.offer(node.right);
                }              
            }
        }
        return root;
    }
}

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