LeetCode - Serialize and Deserialize Binary Tree

解法一：recursion DFS

解法二：non-recursion BFS

/**
 * 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) {
        if(!root) return "";
        queue<TreeNode*> temp;
        temp.push(root);
        string res;
        while(!temp.empty()){
            TreeNode* t = temp.front(); temp.pop();
            if(t==NULL) res+="null|";
            else {
                res+=to_string(t->val)+"|";
                temp.push(t->left);
                temp.push(t->right); 
            }
        }
        return res;
    }

    // Decodes your encoded data to tree.
    TreeNode* deserialize(string data) {
        if(data.empty()) return nullptr;
        
        int start=0,end=0;
        queue<TreeNode*> temp;
        TreeNode* res;
        int size = data.size();
        int f=0;
        while(end!=(size-1)){
            end = data.find_first_of('|', start);
            string t = data.substr(start, end-start);
            if(temp.empty()){
                TreeNode* node = new TreeNode(stoi(t));
                res = node;
                temp.push(node);
            }else{
                TreeNode* node = temp.front();
                if(!f) {
                    f=1;
                    if(t!="null"){
                        node->left = new TreeNode(stoi(t));
                        temp.push(node->left);
                    }
                }
                else{
                    f=0;
                    if(t!="null"){
                        node->right = new TreeNode(stoi(t));
                        temp.push(node->right);
                    }
                    temp.pop();
                }
            }
            start = end+1;
        }
        return res;
    }
};

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

use istringstream 优化

class Codec {
public:
    // Encodes a tree to a single string.
    string serialize(TreeNode* root) {
        ostringstream out;
        queue<TreeNode*> q;
        if (root) q.push(root);
        while (!q.empty()) {
            TreeNode *t = q.front(); q.pop();
            if (t) {
                out << t->val << ' ';
                q.push(t->left);
                q.push(t->right);
            } else {
                out << "# ";
            }
        }
        return out.str();
    }
    // Decodes your encoded data to tree.
    TreeNode* deserialize(string data) {
        if (data.empty()) return nullptr;
        istringstream in(data);
        queue<TreeNode*> q;
        string val;
        in >> val;
        TreeNode *res = new TreeNode(stoi(val)), *cur = res;
        q.push(cur);
        while (!q.empty()) {
            TreeNode *t = q.front(); q.pop();
            if (!(in >> val)) break;
            if (val != "#") {
                cur = new TreeNode(stoi(val));
                q.push(cur);
                t->left = cur;
            }
            if (!(in >> val)) break;
            if (val != "#") {
                cur = new TreeNode(stoi(val));
                q.push(cur);
                t->right = cur;
            }
        }
        return res;
    }
};

spend tons of time on this stupid bug

/**
 * 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) {
        if(!root) return "";
        queue<TreeNode*> temp;
        temp.push(root);
        string res;
        while(!temp.empty()){
            int s = temp.size();
            for(int i=0;i<s;i++){
                TreeNode* t = temp.front(); temp.pop();
                if(t==NULL) res+="null|";
                else {
                    res+=to_string(t->val)+"|";
                    temp.push(t->left);
                    temp.push(t->right); 
                }
            }
        }
        return res;
    }

    // Decodes your encoded data to tree.
    TreeNode* deserialize(string data) {

        int size = data.size();
        if(size==0) return NULL;
        int start=0,end=0;
        
        queue<TreeNode*> temp;
        TreeNode* res;
        int f=0;
        while(end!=(size-1)){
            int end = data.find_first_of('|', start);
            string t = data.substr(start, end-start);
            if(temp.empty()){
                TreeNode* node = new TreeNode(stoi(t));
                res = node;
                temp.push(node);
            }else{
                TreeNode* node = temp.front();
                if(!f) {
                    f=1;
                    if(t!="null"){
                        node->left = new TreeNode(stoi(t));
                        temp.push(node->left);
                    }
                }
                else{
                    f=0;
                    if(t!="null"){
                        node->right = new TreeNode(stoi(t));
                        temp.push(node->right);
                    }
                    temp.pop();
                }
            }
            start = end+1;
        }
        return res;
    }
};

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