leecode第二百九十七题（二叉树的序列化与反序列化）

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Codec {
public:

    // Encodes a tree to a single string.
    string serialize(TreeNode* root) {//结果并不是层序
        if (root == NULL)
            return "#_";
        string res = to_string(root->val) + "_";
        res += serialize(root->left);
        res += serialize(root->right);
        return res;
    }

    // Decodes your encoded data to tree.
    TreeNode* deserialize(string data) {//先打入一个队列里
        stringstream ss(data);
        string item;
        queue<string> q;
        while (getline(ss, item, '_')) 
            q.push(item);
        return helper(q);
    }
    
    TreeNode* helper(queue<string>& q)//对队列进行反序列化
    {
        string val = q.front();
        q.pop();
        if (val == "#")
            return NULL;
        TreeNode* head = new TreeNode(stoi(val));
        head->left = helper(q);
        head->right = helper(q);
        return head;
    }
};

// Your Codec object will be instantiated and called as such:
// Codec codec;
// codec.deserialize(codec.serialize(root));

分析：

层序遍历。