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.
Clarification: The input/output format is the same as how LeetCode serializes a binary tree. You do not necessarily need to follow this format, so please be creative and come up with different approaches yourself.
The number of nodes in the tree is in the range [0, 104].
-1000 <= Node.val <= 1000
ac1: 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) {
// edge cases
if (root == null) return "null";
StringBuilder sb = new StringBuilder();
Queue<TreeNode> q = new LinkedList<>();
q.offer(root);
while (!q.isEmpty()) {
TreeNode h = q.poll();
if (h == null) {
sb.append("null,");
} else {
sb.append("" + h.val + ",");
q.offer(h.left);
q.offer(h.right);
}
}
sb.setLength(sb.length()-1); // remove last ","
return sb.toString();
}
// Decodes your encoded data to tree.
public TreeNode deserialize(String data) {
String[] s = data.split(",");
if ("null".equals(s[0])) return null;
TreeNode root = new TreeNode(Integer.parseInt(s[0])); // set root
Queue<TreeNode> q = new LinkedList<>();
q.offer(root);
int i = 1;
while(!q.isEmpty()) {
TreeNode h = q.poll();
String l = s[i++];
h.left = "null".equals(l) ? null : new TreeNode(Integer.parseInt(l));
String r = s[i++];
h.right = "null".equals(r) ? null : new TreeNode(Integer.parseInt(r));
if (h.left != null) q.offer(h.left);
if (h.right != null) q.offer(h.right);
}
return root;
}
}
// Your Codec object will be instantiated and called as such:
// Codec codec = new Codec();
// codec.deserialize(codec.serialize(root));
/*
1. BFS
2. DFS, pre-order
*/
ac2: DFS pre-order
/**
* 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();
seri(root, sb);
return sb.toString();
}
private void seri(TreeNode node, StringBuilder sb) {
// exit
if (node == null) {
sb.append("null,");
return;
}
sb.append("" + node.val + ",");
seri(node.left, sb);
seri(node.right, sb);
}
// Decodes your encoded data to tree.
public TreeNode deserialize(String data) {
Queue<String> q = new LinkedList<>();
for (String s : data.split(",")) {
q.offer(s);
}
return dese(q);
}
private TreeNode dese(Queue<String> q) {
String str = q.poll();
TreeNode root = "null".equals(str) ? null : new TreeNode(Integer.parseInt(str));
if (root != null) {
root.left = dese(q);
root.right = dese(q);
}
return root;
}
}
// Your Codec object will be instantiated and called as such:
// Codec codec = new Codec();
// codec.deserialize(codec.serialize(root));
/*
1. BFS
2. DFS, pre-order
*/
