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.

答案

public class Codec {

    public String serialize(TreeNode root) {
        if(root == null) return "";
        String str = Integer.toString(root.val);
        if(root.left == null && root.right == null) return str;
        if(root.left == null)
            str += "()";
        else
            str += "(" + serialize(root.left) + ")";

        if(root.right != null)
            str += "(" + serialize(root.right) + ")";
        return str;
    }

    private int find_matching_righ_paren(String data, int left) {
        int count = 0;
        for(int i = left + 1; i < data.length(); i++) {
            if(data.charAt(i) == ')') {
                if(count == 0) return i;
                else count--;
            }
            if(data.charAt(i) == '(') count++;
        }
        return -1;
    }
    // Decodes your encoded data to tree.
    public TreeNode deserialize(String data) {
        if(data.equals("")) return null;
        TreeNode t = null;

        // Find first left paren
        int first_left_paren = data.indexOf('(', 0);
        if(first_left_paren == -1) return new TreeNode(Integer.parseInt(data));
        else t = new TreeNode(Integer.parseInt(data.substring(0, first_left_paren)));

        // Find the right paren that matches first left paren
        int first_right_paren = find_matching_righ_paren(data, first_left_paren);
        t.left = deserialize(data.substring(first_left_paren + 1, first_right_paren));

        // Find first left paren after the above right paren
        int second_left_paren = data.indexOf('(', first_right_paren + 1);
        if(second_left_paren != -1) {
            // Find the right paren that matches the above left paren
            int second_right_paren = find_matching_righ_paren(data, second_left_paren);
            t.right = deserialize(data.substring(second_left_paren + 1, second_right_paren));
        }
        return t;
    }
}