二叉树遍历（前中后）

二叉树前序遍历：

/*** Definition for binary tree* struct TreeNode {*     int val;*     TreeNode *left;*     TreeNode *right;*     TreeNode(int x) : val(x), left(NULL), right(NULL) {}* };*/
class Solution {
public:vector<int> preorderTraversal(TreeNode *root) {vector<int> res;if(root==NULL)return res;stack<TreeNode *> sta;sta.push(root);while(!sta.empty()){TreeNode *tmp=sta.top();sta.pop();res.push_back(tmp->val);if(tmp->right)sta.push(tmp->right);if(tmp->left)sta.push(tmp->left);}return res;}
/**
void preorder(vector<int> &res, TreeNode * root)
{if(root==NULL)return;res.push_back(root->val);preorder(res,root->left);preorder(res,root->right);
}vector<int> preorderTraversal(TreeNode *root) {vector<int> res;preorder(res,root);return res;}
*/
};

　　

 

二叉树中序遍历：

/*** Definition for binary tree* struct TreeNode {*     int val;*     TreeNode *left;*     TreeNode *right;*     TreeNode(int x) : val(x), left(NULL), right(NULL) {}* };*/
class Solution {
public:
vector<int> inorderTraversal(TreeNode *root) 
{vector<int> res;if(root==NULL)return res;TreeNode *p=root;stack<TreeNode *> sta;while(p!=NULL||!sta.empty()){while(p!=NULL){sta.push(p);p=p->left;}if(!sta.empty()){p=sta.top();sta.pop();res.push_back(p->val);p=p->right;}}return res;
}
/*
void inorder(TreeNode *root, vector<int> &res)
{if(root==NULL)return;inorder(root->left,res);res.push_back(root->val);inorder(root->right,res);return;
}vector<int> inorderTraversal(TreeNode *root) {vector<int> res;inorder(root,res);return res;}
*/
};

　　

二叉树后序遍历：

/*** Definition for binary tree* struct TreeNode {*     int val;*     TreeNode *left;*     TreeNode *right;*     TreeNode(int x) : val(x), left(NULL), right(NULL) {}* };*/
class Solution {
public:vector<int> postorderTraversal(TreeNode *root) {vector<int> res;if(root==NULL)return res;map<TreeNode *, int> smap;smap[root]=0;stack<TreeNode *> sta;sta.push(root);while(!sta.empty()){TreeNode *p=sta.top();if((!p->right&&!p->left)||smap.count(p->right)||smap.count(p->left)){res.push_back(p->val);smap[p]=1;sta.pop();}else{if(p->right&&!smap.count(p->right)){sta.push(p->right);smap[p->right]=0;}if(p->left&&!smap.count(p->left)){sta.push(p->left);smap[p->left]=0;}}}return res;}
/**
void postorder(vector<int> & res,TreeNode *root)
{if(root==NULL)return;postorder(res,root->left);postorder(res,root->right);res.push_back(root->val);
}vector<int> postorderTraversal(TreeNode *root) {vector<int> res;postorder(res,root);return res;}
*/
};