[Leetcode] 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"]

分析：深度优先搜索

/**
 * 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> result;
    
    vector<string> binaryTreePaths(TreeNode* root) {
        if (root == NULL) return result;
        
        string s;
        binaryTreePaths(root, s+to_string(root->val));
        return result;
    }
    
    void binaryTreePaths(TreeNode* root, string path) {
        if (root->left == NULL && root->right == NULL) {
            result.push_back(path);
            return;
        } else {
            if (root->left != NULL)
                binaryTreePaths(root->left, path+"->"+to_string(root->left->val));
            
            if (root->right != NULL)
                binaryTreePaths(root->right, path+"->"+to_string(root->right->val));
        }

    }
};