力扣-二叉树-144.145. 94 前、后、中序遍历，

思路

三种递归遍历方式

前序遍历代码

class Solution {
public:
    void preTree(vector<int> &nums, TreeNode* node){
        if(node == nullptr) return;
        nums.push_back(node->val);
        preTree(nums, node->left);
        preTree(nums, node->right);
        return;
    }

    vector<int> preorderTraversal(TreeNode* root) {
        vector<int> res;

        preTree(res, root);

        return res;
    }
};

后序遍历代码

class Solution {
public:

    void postTree(vector<int> &nums, TreeNode* node){
        if(node == nullptr) return;
        postTree(nums, node->left);
        postTree(nums, node->right);
        nums.push_back(node->val);
        return;
    }

    vector<int> postorderTraversal(TreeNode* root) {
        vector<int> res;

        postTree(res, root);

        return res;
    }
};

中序遍历代码

class Solution {
public:

    void inorderTree(vector<int> &nums, TreeNode* node){
        if(node == nullptr) return;
        inorderTree(nums, node->left);
        nums.push_back(node->val);

        inorderTree(nums, node->right);
        return;
    }

    vector<int> inorderTraversal(TreeNode* root) {
        vector<int> res;

        inorderTree(res, root);

        return res;
    }
};