15算法课程 257. 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"]

solution:

写两个binaryTreePaths函数，第一个使用递归方法构造题目要求的字符串，这个函数需要合理选择参数；第二个函数用来返回结果

code:

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