297. Serialize and Deserialize Binary Tree
Time = O(n), Space = O(n). 参考题解
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/**
* 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.
// root: [1,2,3,null,null,4,5]
// sb: 1,2,#,#,3,4,#,#,5,#,#,
public String serialize(TreeNode root) {
StringBuilder sb = new StringBuilder();
serializeHelper(root, sb);
return sb.toString();
}
private void serializeHelper(TreeNode root, StringBuilder sb) {
if (root == null) {
sb.append("#").append(",");
return;
}
sb.append(root.val).append(",");
serializeHelper(root.left, sb);
serializeHelper(root.right, sb);
}
// Decodes your encoded data to tree.
public TreeNode deserialize(String data) {
Deque<String> queue = new LinkedList<>(Arrays.asList(data.split(",")));
return deserializeHelper(queue);
}
private TreeNode deserializeHelper(Deque<String> queue) {
if (queue.isEmpty()) {
return null;
}
String val = queue.poll();
if (val.equals("#")) {
return null;
}
TreeNode root = new TreeNode(Integer.valueOf(val));
root.left = deserializeHelper(queue);
root.right = deserializeHelper(queue);
return root;
}
}
// Your Codec object will be instantiated and called as such:
// Codec codec = new Codec();
// codec.deserialize(codec.serialize(root));