297 Serialize and Deserialize Binary Tree
Problem:
Serialization is the process of converting a data structure or object into a sequence of bits so that it can be stored in a file or memory buffer, or transmitted across a network connection link to be reconstructed later in the same or another computer environment.
Design an algorithm to serialize and deserialize a binary tree. There is no restriction on how your serialization/deserialization algorithm should work. You just need to ensure that a binary tree can be serialized to a string and this string can be deserialized to the original tree structure.
For example, you may serialize the following tree
1
/ \
2 3
/ \
4 5
as "[1,2,3,null,null,4,5]", just the same as how LeetCode OJ serializes a binary tree. You do not necessarily need to follow this format, so please be creative and come up with different approaches yourself. Note: Do not use class member/global/static variables to store states. Your serialize and deserialize algorithms should be stateless.
Solutions:
BFS
/**
* 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) {
StringBuilder sb = new StringBuilder();
Queue<TreeNode> q = new LinkedList<TreeNode>();
q.add(root);
while (!q.isEmpty()) {
TreeNode node = q.poll();
if (node == null) {
sb.append("# ");
}
else {
sb.append(node.val + " ");
q.add(node.left);
q.add(node.right);
}
}
return sb.toString().trim();
}
// Decodes your encoded data to tree.
public TreeNode deserialize(String data) {
if (data.equals("#")) {
return null;
}
String[] nodes = data.split(" ");
TreeNode root = null;
Queue<TreeNode> q = new LinkedList<TreeNode>();
for (int i = 0; i < nodes.length; i ++) {
if (q.isEmpty()) {
root = new TreeNode(Integer.parseInt(nodes[i]));
q.add(root);
}
else {
TreeNode left = null;
TreeNode right = null;
if (!nodes[i].equals("#")){
left = new TreeNode(Integer.parseInt(nodes[i]));
q.add(left);
}
if (!nodes[i + 1].equals("#")){
right = new TreeNode(Integer.parseInt(nodes[i + 1]));
q.add(right);
}
TreeNode parent = q.poll();
parent.left = left;
parent.right = right;
i = i + 1;
}
}
return root;
}
}
// Your Codec object will be instantiated and called as such:
// Codec codec = new Codec();
// codec.deserialize(codec.serialize(root));
/**
* 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) {
StringBuilder sb = new StringBuilder();
serialize(root, sb);
return sb.toString().trim();
}
private void serialize(TreeNode node, StringBuilder sb) {
if (node == null) {
sb.append("# ");
}
else {
sb.append(node.val+ " ");
serialize(node.left, sb);
serialize(node.right, sb);
}
}
// Decodes your encoded data to tree.
public TreeNode deserialize(String data) {
String[] nodes = data.split(" ");
return deserialize(nodes, new int[]{0});
}
private TreeNode deserialize(String[] nodes, int[] index) {
if (nodes[index[0]].equals("#")) {
index[0] ++;
return null;
}
TreeNode node = new TreeNode(Integer.parseInt(nodes[index[0]]));
index[0] ++;
node.left = deserialize(nodes, index);
node.right = deserialize(nodes, index);
return node;
}
}
// Your Codec object will be instantiated and called as such:
// Codec codec = new Codec();
// codec.deserialize(codec.serialize(root));