[LeetCode]94. Binary Tree Inorder Traversal（DFS）

题目链接：https://leetcode.com/problems/binary-tree-inorder-traversal/?tab=Description

题意：中序遍历。

class Solution {
public:
    vector<int> ret;
    void dfs(TreeNode* rt) {
        if (!rt) return;
        dfs(rt -> left);
        ret.push_back(rt -> val);
        dfs(rt -> right);
    }
    vector<int> inorderTraversal(TreeNode* rt) {
        ret.clear();
        dfs(rt);
        return ret;
    }
};