Leetcode 257 Binary Tree Paths 二叉树 DFS

找到所有根到叶子的路径

深度优先搜索（DFS）， 即二叉树的先序遍历。

 /**
  * Definition for a binary tree node.
  * struct TreeNode {
  *     int val;
  *     TreeNode *left;
  *     TreeNode *right;
  *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
  * };
  */
 class Solution {
 public:
     vector<string> vs_;
     void dfs(TreeNode* root, string s){
         if(!root) return;
         if(!root->left && !root->right){
            char t[] = "";
            sprintf(t, "->%d", root->val);
            vs_.push_back(s + string(t));
            return;
         }
         else{
            char t[] = "";
            sprintf(t, "->%d", root->val);
            dfs(root->left, s + string(t));
            dfs(root->right, s + string(t));
         }
     }
     vector<string> binaryTreePaths(TreeNode* root) {
         vs_.clear();
         if(!root) return vs_;
         char t[] = "";
         sprintf(t, "%d", root->val);
         string s(t);
         if(!root->left && !root->right){
             vs_.push_back(s);
             return vs_;
         }
         dfs(root->left, s);
         dfs(root->right, s);
         return vs_;
     }
 };