树的非递归遍历

最新推荐文章于 2021-09-12 14:48:58 发布

原创最新推荐文章于 2021-09-12 14:48:58 发布 · 403 阅读

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#遍历

1.前序

/**
 * 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> v;
                TreeNode* p = root;
                stack<TreeNode*> s;
                while(p || !s.empty()){
                      while(p){
                          <span style="color:#ff0000;">v.push_back(p->val);/* 访问根节点 */</span>
                          s.push(p);
                          p = p->left;/* 访问左子树 */
                      }
                      if(!s.empty()){
                          p = s.top()->right;/* 访问右子树 */
                          //v.push_back(s.top()->val);
                          s.pop();
                      }
                }
                return v;
    }
};

2. 中序

/**
 * 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> v;
                TreeNode* p = root;
                stack<TreeNode*> s;
                while(p || !s.empty()){
                      while(p){
                         // v.push_back(p->val);
                          s.push(p);
                          p = p->left;/* 访问左子树 */
                      }
                      if(!s.empty()){
                         <span style="color:#ff0000;"> <span style="font-family: Arial, Helvetica, sans-serif;">v.push_back(s.top()->val); /* 访问根节点 */</span></span><pre code_snippet_id="464620" snippet_file_name="blog_20140905_2_3449297" name="code" class="cpp">                          p = s.top()->right;/* 访问右子树 */

s.pop(); } } return v; }};

3.后序

/**
 * 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> v;
	      stack<TreeNode*>st;
	      TreeNode* p = root;
	      while(p || !st.empty()){
	           while(p){
	               st.push(p);
	               p = p->left;/*访问左子树*/
	           }
	           TreeNode* pre = NULL;
	           while(!st.empty() && st.top()->right == pre){/* 当右子树为空或者右子树已经访问过时，输出根节点，此时左子树已经访问完成*/
	                 v.push_back(st.top()->val);
	                 pre = st.top();
	                 st.pop();
	           }
	           if(st.empty()) break;
	           p = st.top()->right;/*访问右子树*/
	      }
	      return v;
    }
};