Binary Tree Paths

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"]

/**
 * 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> binaryTreePaths(TreeNode* root) {
        vector<string> vs;
        if (root == NULL) return vs;
        if (root->left == NULL && root->right == NULL) {
            char buff[124];
            sprintf(buff, "%d", root->val);
            vs.push_back(buff);
            return vs;
        }
        if (root->left) {
            vector<string> lefts = binaryTreePaths(root->left);
            for (int i = 0; i < lefts.size(); i++) {
                char *buff = new char[lefts[i].size()+56];
                sprintf(buff, "%d->%s", root->val, lefts[i].c_str());
                vs.push_back(buff);
                delete[] buff;
            }
        }
        if (root->right) {
            vector<string> rights = binaryTreePaths(root->right);
            for (int i = 0; i < rights.size(); i++) {
                char *buff = new char[rights[i].size()+56];
                sprintf(buff, "%d->%s", root->val, rights[i].c_str());
                vs.push_back(buff);
                delete[] buff;
            }
        }
        return vs;
    }
};

• 使用递归时，确定返回值是什么东西，然后后面根据返回的东西进行处理

 

 

/**
   * 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> binaryTreePaths(TreeNode* root) 
    {
      vector<string> results;
      visitTreeNode(root, "", results);
      return results;
    }
  private:
    void visitTreeNode(TreeNode* node, string path, vector<string>& result)
    {
      if(node == nullptr) return;
      if (!path.empty())                //检测之前的路径是不是为空；
      {                    //如果为空，则为第一个路径，不许要加->
        path += "->";                //如果不为空则需要在后面加->
      }
      path += int2Str(node->val);            //必须使用将int型转换为string型
      if (node->left == nullptr && node->right == nullptr)
      {
        result.push_back(path);
      }
      else
      {
        if (node->left != nullptr)
        {
          visitTreeNode(node->left, path, result);
        }
        if (node->right != nullptr)
        {
          visitTreeNode(node->right, path, result);
        }
      }
    }
    std::string int2Str(int nValue)        
    {
      ostringstream ss;
      ss << nValue;            //直接给string型赋值是不可以的，必须通过流转换
      return ss.str();
    }
  };