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  • 449. Serialize and Deserialize BST

    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 search tree. There is no restriction on how your serialization/deserialization algorithm should work. You just need to ensure that a binary search tree can be serialized to a string and this string can be deserialized to the original tree structure.

    The encoded string should be as compact as possible.

    Note: Do not use class member/global/static variables to store states. Your serialize and deserialize algorithms should be stateless.

    serialize用preorder traverse,deserialize用queue作辅助,左右分别递归

    serialize      -- time: O(n), space: O(height)

    deserialize  -- time: O(n), space: O(n)

    /**
     * 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) {
            if(root == null) {
                return "";
            }
            StringBuilder sb = new StringBuilder();
            preorder(root, sb);
            return sb.toString();
        }
        
        public void preorder(TreeNode root, StringBuilder sb) {
            if(root == null) {
                return;
            }
            sb.append(root.val).append(" ");
            preorder(root.left, sb);
            preorder(root.right, sb);
        }
    
        // Decodes your encoded data to tree.
        public TreeNode deserialize(String data) {
            if(data == "") {
                return null;
            }
            String[] vals = data.split(" ");
            Queue<Integer> q = new LinkedList<>();
            for(String val : vals) {
                q.offer(Integer.parseInt(val));
            }
            return deserialize(q);
        }
        
        public TreeNode deserialize(Queue<Integer> q) {
            if(q.isEmpty()) {
                return null;
            }
            TreeNode root = new TreeNode(q.poll());
            Queue<Integer> smallerQ = new LinkedList<>();
            while(!q.isEmpty() && q.peek() < root.val) {
                smallerQ.offer(q.poll());
            }
            root.left = deserialize(smallerQ);
            root.right = deserialize(q);
            return root;
        }
    }
    
    // Your Codec object will be instantiated and called as such:
    // Codec codec = new Codec();
    // codec.deserialize(codec.serialize(root));
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  • 原文地址:https://www.cnblogs.com/fatttcat/p/10202259.html
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