二叉树的三种遍历

/**
 * struct TreeNode {
 *	int val;
 *	struct TreeNode *left;
 *	struct TreeNode *right;
 * };
 */

class Solution {
public:
    /**
     * 
     * @param root TreeNode类 the root of binary tree
     * @return int整型vector<vector<>>
     */
    vector<int> pre;
    vector<int> mid;
    vector<int> post;
    
    void preOrder(TreeNode* root)
    {
        if(root == NULL) return;
        pre.push_back(root->val);
        preOrder(root->left);
        preOrder(root->right);
    }
    void midOrder(TreeNode* root)
    {
        if(root == NULL) return ;
        midOrder(root->left);
        mid.push_back(root->val);
        midOrder(root->right);
    }
    void rearOrder(TreeNode* root)
    {
        if(root == NULL) return;
        rearOrder(root->left);
        rearOrder(root->right);
        post.push_back(root->val);
    }
    vector<vector<int> > threeOrders(TreeNode* root) {
        // write code here
        vector<vector<int> > result;
        preOrder(root);
        midOrder(root);
        rearOrder(root);
        result ={pre,mid,post};
        return result;
    }
};

总结来看：
1，代码简洁
2，思路清晰：
前序遍历：中左右
中序遍历：左中右
后序遍历：左中右
3，容器的添加方式的一种写法
vector<vector > result; result ={pre,mid,post};