leetcode 297二叉树的序列化与反序列化

Posted 2021-12-09 joelwang

 

采用层序遍历的顺序，储存每一层的值，不存在的或者NULL值用#代替，每个位置以‘/‘结束

/**
 * 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) {
        string res;
        queue<TreeNode*> q;
        q.push(root);
        int flag=1;
        while(flag){
            flag=0;
            int k=q.size();
            for(int i=0;i<k;i++){
                TreeNode* p=q.front();
                q.pop();
                if(p==NULL){
                    res.push_back(‘#‘);
                    q.push(NULL);
                    q.push(NULL);
                }else{
                    int value=p->val;
                    if(value<0) {res.push_back(‘-‘);value=-value;}
                    stack<char> s;
                    if(value==0) s.push(‘0‘);
                    while(value){
                        int e=value%10;
                        s.push(e+‘0‘);value=value/10;
                    }
                    while(!s.empty()){
                        res.push_back(s.top());s.pop();
                    }
                    q.push(p->left);
                    q.push(p->right);
                    if(p->left||p->right) flag=1;
                }
                res.push_back(‘/‘);
            }
        }
        cout<<res<<endl;
        return res;
    }

    // Decodes your encoded data to tree.
    TreeNode* deserialize(string data) {
        if(data.size()==0) return NULL;
        if(data.size()==2&&data[0]==‘#‘)return NULL;
        int len=data.size();
        vector<TreeNode*> v;
        for(int i=0;i<len;i++){
            if(data[i]==‘/‘)continue;
            TreeNode* p=NULL;
            
            if(data[i]!=‘#‘){
                int value=0;
                int flag=1;
                if(data[i]==‘-‘) {flag=-1;i++;}
                while(data[i]!=‘/‘){
                    value=10*value+data[i]-‘0‘;
                    i++;
                }
                value=flag*value;
                p=new TreeNode(value);
            }
            
            v.push_back(p);
        }
        for(int i=0;i<(v.size()-1)/2;i++){
            if(v[i]!=NULL){
                v[i]->left=v[2*i+1];
                v[i]->right=v[2*i+2];
            }
        }
        return v[0];
    }
};

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

 测试例子如下：

样例通过为47/48，一个深度为1000的偏二叉树没有通过；