题解 | #实现二叉树先序，中序和后序遍历# | C++

/**
 * struct TreeNode {
 *	int val;
 *	struct TreeNode *left;
 *	struct TreeNode *right;
 *	TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 * };
 */
#include <vector>
class Solution {
public:
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     * 
     * @param root TreeNode类 the root of binary tree
     * @return int整型vector<vector<>>
     */
    vector<vector<int> > threeOrders(TreeNode* root) {
        vector<vector<int>> ans = {{},{},{}};
        dfs(root, ans);
        return ans;
    }

    void dfs(TreeNode*node, vector<vector<int>>& ans) {
        if (node) {
            ans[0].push_back(node->val);
            dfs(node->left, ans);
            ans[1].push_back(node->val);
            dfs(node->right, ans);
            ans[2].push_back(node->val);
        }
    }
};