NC45 #实现二叉树先序，中序和后序遍历#

递归：

/**
 * 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> preVec;
    vector<int> inVec;
    vector<int> postVec;
    vector<vector<int> > vec;
    void preOrder(TreeNode* root)
    {
        if(root)
        {
            preVec.push_back(root->val);
            preOrder(root->left);
            preOrder(root->right);
        }
    }

    void inOrder(TreeNode* root)
    {
        if(root)
        {
            inOrder(root->left);
            inVec.push_back(root->val);
            inOrder(root->right);
        }
    }

    void postOrder(TreeNode* root)
    {
        if(root)
        {
            postOrder(root->left);
            postOrder(root->right);
            postVec.push_back(root->val);
        }
    }

    vector<vector<int> > threeOrders(TreeNode* root) {
        preOrder(root);
        inOrder(root);
        postOrder(root);
        vec.push_back(preVec);
        vec.push_back(inVec);
        vec.push_back(postVec);
        return vec;
    }
};