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题目:
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.
解答:
public class Codec {
private String spliter = ",";
//用一个特殊的符号来表示null的情况
private String NN = "X";
// Encodes a tree to a single string.
public void BuildString(StringBuilder sb, TreeNode root) {
if (root == null) {
sb.append("X").append(spliter);
} else {
//这是按先序遍历来存root到string中去
sb.append(root.val).append(spliter);
BuildString(sb, root.left);
BuildString(sb, root.right);
}
}
public String serialize(TreeNode root) {
StringBuilder sb = new StringBuilder();
BuildString(sb, root);
return sb.toString();
}
// Decodes your encoded data to tree.
public TreeNode BuildTree(Deque<String> nodes) {
String node = nodes.remove();
if (node.equals(NN)) {
return null;
} else {
//Integer.valueOf("String");
TreeNode root = new TreeNode(Integer.valueOf(node));
root.left = BuildTree(nodes);
root.right = BuildTree(nodes);
return root;
}
}
public TreeNode deserialize(String data) {
//deque这里用linkedlist为interface,其包含了几乎所有resizable array
Deque<String> nodes = new LinkedList<>();
//这里还是挺多知识点的,String.split()后是一个String[], Arrays.asList()可以把数组变成list, nodes.addAll()则是把list加到nodes这个list的中去
nodes.addAll(Arrays.asList(data.split(spliter)));
return BuildTree(nodes);
}
}
// Your Codec object will be instantiated and called as such:
// Codec codec = new Codec();
// codec.deserialize(codec.serialize(root));
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