257.BinaryTreePaths

257.BinaryTreePaths

LeetCode

题目描述

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”]

解题思路

此题的思路就是前序遍历树，记录下每一个访问过的节点，若节点为叶子节点，则把这条路径加入到vector中，然后把这个点的值删除掉，接着访问下一个节点。每次返回上一层，就需要把这一层的节点+->删除掉。

代码

 /**     * 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;            if(!root) return results;            string result;            PreOrder(root, results, result);            return results;        }        void PreOrder(TreeNode* root, vector<string>& results, string& result)        {            string::iterator it;            if(!root) return;            if(root->left == nullptr && root->right == nullptr)            {                string temp = to_string(root->val);                result = result + temp;                results.push_back(result);                //这里容易出错，叶子节点只需要减去叶子节点的长度                it = result.end() - temp.length();                result.erase(it,result.end());                return;            }            string temp = to_string(root->val);            result = result + temp + "->";            PreOrder(root->left, results, result);            PreOrder(root->right, results, result);            //如果不是叶子节点，需要减去本身的长度+"->"的length为2.            it = result.end() - (temp.length() + 2);            result.erase(it,result.end());        }    };