题解 | #实现二叉树先序，中序和后序遍历#

• 递归进行前、中、后序遍历；
• 记录每种遍历的结果。

/**
 * 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<vector<int>> result;
    vector<int> vec;
    void preOrder(TreeNode* root, vector<int>& vec) {
        if (root == NULL) return;
        vec.push_back(root->val);
        if (root->left) preOrder(root->left, vec);
        if (root->right) preOrder(root->right, vec);
    }
    void minOrder(TreeNode* root, vector<int>& vec) {
        if (root == NULL) return;
        if (root->left) minOrder(root->left, vec);
        vec.push_back(root->val);
        if (root->right) minOrder(root->right, vec);
    }
    void postOrder(TreeNode* root, vector<int>& vec) {
        if (root == NULL) return;
        if (root->left) postOrder(root->left, vec);
        if (root->right) postOrder(root->right, vec);
        vec.push_back(root->val);
    }
    vector<vector<int> > threeOrders(TreeNode* root) {
        // write code here
        result.clear();
        vec.clear();
        preOrder(root, vec);
        result.push_back(vec);
        vec.clear();
        minOrder(root, vec);
        result.push_back(vec);
        vec.clear();
        postOrder(root, vec);
        result.push_back(vec);
        return result;
    }
};