[LeetCode] Binary Tree Paths

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"]

Credits:

Special thanks to @jianchao.li.fighter for adding this problem and creating all test cases.
解题思路：

这道题题意是返回二叉树中所有从根到叶的路径。用递归法做比较方便。

/**
* 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> result;
helper(root, "", result);
return result;
}

void helper(TreeNode* root, string item, vector<string>& result){
if(root==NULL){
return;
}
item = item+std::to_string(root->val);
if(root->left!=NULL){
helper(root->left, item + "->", result);
}
if(root->right!=NULL){
helper(root->right, item + "->", result);
}
if(root->left==NULL&&root->right==NULL){
result.push_back(item);
}
}
};