Leetcode 257. Binary Tree Paths

257. Binary Tree Paths

• Total Accepted: 56430
• Total Submissions: 185972
• Difficulty: Easy

Given a binary tree, return all root-to-leaf paths.

For example, given the following binary tree:

  1
 /   
2     3
 
  5

All root-to-leaf paths are:

["1->2->5", "1->3"]

思路：DFS。遇到叶节点就push_back。注意c++中，to_string()可以直接将int转化为string类型。

代码：

形式一：

class Solution {
public:
    void binaryTreePaths(vector<string>& res,TreeNode* root,string str){
        if(!root) return;
        str=str+to_string(root->val);
        if(!root->left&&!root->right) res.push_back(str);
        binaryTreePaths(res,root->left,str+"->");
        binaryTreePaths(res,root->right,str+"->");
    }
    vector<string> binaryTreePaths(TreeNode* root) {
        vector<string> res;
        binaryTreePaths(res,root,"");
        return res;
    }
};

形式二：

class Solution {
public:
    void binaryTreePaths(vector<string>& res,TreeNode* root,string str){
        if(!root->left&&!root->right) res.push_back(str);
        if(root->left) binaryTreePaths(res,root->left,str+"->"+to_string(root->left->val));
        if(root->right) binaryTreePaths(res,root->right,str+"->"+to_string(root->right->val));
    }
    vector<string> binaryTreePaths(TreeNode* root) {
        vector<string> res;
        if(root) binaryTreePaths(res,root,to_string(root->val));
        return res;
    }
};