[297. Serialize and Deserialize Binary Tree] #lc_297

297_0812.java

public class Codec {
    private static final String SEP = ",";
    private static final String NULL = "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(NULL).append(SEP);
        } else {
            sb.append(node.val).append(SEP);
            buildString(node.left, sb);
            buildString(node.right, sb);
        }
    }
    
    // Decodes your encoded data to tree.
    public TreeNode deserialize(String data) {
        Deque<String> values = new LinkedList<>();
        values.addAll(Arrays.asList(data.split(SEP)));
        return buildTree(values);
    }
    
    public TreeNode buildTree(Deque<String> values) {
        String val = values.removeFirst();
        if (val.equals(NULL)) return null;
        
        TreeNode node = new TreeNode(Integer.parseInt(val));
        
        node.left = buildTree(values);
        node.right = buildTree(values);
        return node;
    }
}