preorder-postorder- tree - via stack

最新推荐文章于 2021-12-25 18:00:44 发布

转载最新推荐文章于 2021-12-25 18:00:44 发布 · 672 阅读

本文介绍了二叉树的前序遍历和后序遍历算法实现，通过使用栈来辅助完成非递归方式的遍历过程。文章提供了具体的C++代码实现，并详细解释了每种遍历方式的工作原理。

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/**
 * 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> result;
        if(root == NULL)
        return result;
        stack<TreeNode *> stk;
        stk.push(root);
        while(!stk.empty())
        {
            TreeNode * trnd = stk.top();
            result.push_back(trnd->val);
            stk.pop();
            if(trnd->right)
            stk.push(trnd->right);
            if(trnd->left)
            stk.push(trnd->left);
        }
        
        return result;
    }
};

=====================================================================================

/**
 * 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> result;
       if(root==NULL) return result;
      stack<TreeNode *> stk;
      stk.push(root);
      
      while(!stk.empty())
      {
          TreeNode * tmp = stk.top();
          if(tmp->left==NULL && tmp->right==NULL)
          {
              result.push_back(tmp->val);
              stk.pop();
              while(!stk.empty() &&(stk.top()->right == tmp || stk.top()->left == tmp))
              {
                  tmp = stk.top();
                  result.push_back(tmp->val);
                  stk.pop();
              }
          }
          else
          {
              
              if(tmp->right)
              stk.push(tmp->right);
              if(tmp->left)
              stk.push(tmp->left);
          }
      }
      return result;
    }
};

===============================================================================

/**
 * 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> result;
        if(root==NULL) return result;
        stack<TreeNode *> stk;
        TreeNode *node = root;
        while(!stk.empty() ||node)
        {
            while(node!=NULL)
            {
                result.push_back(node->val);
                stk.push(node);//!!!
                node=node->left;
            }
            if(node == NULL)
            {
                node = stk.top();
                stk.pop();
                node=node->right;
            }
        }
    }
};

http://en.wikipedia.org/wiki/Tree_traversal

http://bbs.chinaunix.net/forum.php?mod=viewthread&tid=331522