请用递归方式实现二叉树的先序、中序和后序的遍历打印。
给定一个二叉树的根结点root，请依次返回二叉树的先序，中序和后续遍历(二维数组的形式)。
/*
struct TreeNode {
int val;
struct TreeNode *left;
struct TreeNode *right;
TreeNode(int x) :
val(x), left(NULL), right(NULL) {
}
};*/
class TreeToSequence {
public:
void pre(TreeNode* root, vector<int>& result)
{
if(NULL == root){
return;
}
result.push_back(root->val);
pre(root->left, result);
pre(root->right, result);
}
void mid(TreeNode* root, vector<int>& result)
{
if(NULL == root){
return;
}
mid(root->left, result);
result.push_back(root->val);
mid(root->right, result);
}
void post(TreeNode* root, vector<int>& result)
{
if(NULL == root){
return;
}
post(root->left, result);
post(root->right, result);
result.push_back(root->val);
}
vector<vector<int> > convert(TreeNode* root) {
// write code here
vector<vector<int>> res(3);
pre(root, res[0]);
mid(root, res[1]);
post(root, res[2]);
return res;
}
};
