刷题297. Serialize and Deserialize Binary Tree

一、题目说明

题目297. Serialize and Deserialize Binary Tree，序列号和反序列化二叉树。难度是Hard！

二、我的解答

这个题目用了3个小时，用的非递归遍历算法。用stack实现：

class Codec{
	public:
		// Encodes a tree to a single string.
	    string serialize(TreeNode* root) {
	        //先根遍历二叉树
	        string res;
	        
	        if(root ==NULL) return "[null]";
			stack<TreeNode*> st;
			st.push(root);
			res.append(to_string(root->val));
			res.push_back(',');
				
			while(! st.empty()){
				TreeNode* tmp = st.top();
				st.pop();
				
				if(tmp->left !=NULL){
					res.append(to_string(tmp->left->val));
					res.push_back(',');
				}else{
					res.append("null,");
				}
								
				if(tmp->right !=NULL){
					st.push(tmp->right);
					res.append(to_string(tmp->right->val));
					res.push_back(',');
				}else{
					res.append("null,");
				}
				
				if(tmp->left !=NULL){
					st.push(tmp->left);
				}
			}
			res.pop_back();
			
			return "["+res+"]";
	    }
	    // Decodes your encoded data to tree.
	    TreeNode* deserialize(string data) {
	    	data = data.substr(1, data.size() - 2);
	    	
	    	TreeNode* root =NULL,*p;

	    	int len = data.size();
	    	if(data.compare("null")==0){
	    		return root;
			}
	    	
	        if(!data.empty()){
	        	stack<TreeNode*> st;
	        	int l=0,r=0;
	        	while(data[r]!=','){
	        		r++;
				}
				string str = data.substr(l,r-l);
				//cout<<str<<"->";
				int cur = stoi(str);
				root = new TreeNode(cur);
				st.push(root);
				while(! st.empty()){
					p = st.top();
					st.pop();
					
					//左子树 
					l=r+1,r=l;
		        	while(r<len && data[r]!=','){
		        		r++;
					}
					str = data.substr(l,r-l);
					//cout<<str<<"->";
					if(str.compare("null") !=0){
						cur = stoi(str);
						p->left = new TreeNode(cur);
					}
					
					//右子树 
					l=r+1,r=l;
		        	while(r<len && data[r]!=','){
		        		r++;
					}
					str = data.substr(l,r-l);
					//cout<<str<<"->";
					if(str.compare("null") !=0){
						cur = stoi(str);
						p->right = new TreeNode(cur);
						st.push(p->right);
					}
					
					if(p->left !=NULL){
						st.push(p->left);
					}
				}
				return root;
			}else{
				return root;
			}
	    }
};

性能如下：

Runtime: 40 ms, faster than 83.45% of C++ online submissions for Serialize and Deserialize Binary Tree.
Memory Usage: 32.2 MB, less than 44.83% of C++ online submissions for Serialize and Deserialize Binary Tree.

三、优化措施

无