前序遍历
/**
* Definition for a binary tree node.
* struct TreeNode
* {
* int val;
* TreeNode *left;
* TreeNode *right;
* TreeNode() : val(0), left(nullptr), right(nullptr) {}
* TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
* TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
* };
*/
class Solution {
public:
void f(TreeNode* root, vector<int> &ans)
{
if (root)
{
ans.push_back(root->val);
f(root->left, ans);
f(root->right, ans);
}
}
vector<int> preorderTraversal(TreeNode* root)
{
vector<int> ans;
f(root, ans);
return ans;
}
};
中序遍历
递归写法：
class Solution {
public:
void f(TreeNode* root, vector<int> &ans)
{
if (root)
{
f(root->left, ans);
ans.push_back(root->val);
f(root->right, ans);
}
}
vector<int> inorderTraversal(TreeNode* root)
{
vector<int> ans;
f(root, ans);
return ans;
}
};
非递归写法：
class Solution {
public:
void f(TreeNode* root, vector<int> &ans)
{
stack<TreeNode*> s;
TreeNode *p = root;
while (p || !s.empty())
{
if (p)
{
s.push(p);
p = p->left;
}
else
{
ans.push_back(s.top()->val);
p = s.top()->right;
s.pop();
}
}
}
vector<int> inorderTraversal(TreeNode* root)
{
vector<int> ans;
f(root, ans);
return ans;
}
};
后序遍历
递归写法
class Solution {
public:
void f(TreeNode* root, vector<int> &ans)
{
if (root)
{
f(root->left, ans);
f(root->right, ans);
ans.push_back(root->val);
}
}
vector<int> postorderTraversal(TreeNode* root)
{
vector<int> ans;
f(root, ans);
return ans;
}
};
非递归写法
class Solution {
public:
void f(TreeNode* root, vector<int> &ans)
{
stack<TreeNode*> s;
TreeNode *p = root, *temp = NULL;
while (p || !s.empty())
{
if (p)
{
s.push(p);
p = p->left;
}
else
{
p = s.top();
if (p->right != NULL && p->right != temp) p = p->right;
else
{
ans.push_back(p->val);
s.pop();
temp = p;
p = NULL;
}
}
}
}
vector<int> postorderTraversal(TreeNode* root)
{
vector<int> ans;
f(root, ans);
return ans;
}
};