二叉树前序中序后序非递归写法

最新推荐文章于 2022-10-27 13:32:48 发布

翻译最新推荐文章于 2022-10-27 13:32:48 发布 · 133 阅读

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本文详细介绍了二叉树的前序、中序和后序遍历算法，并通过C++代码实现，深入解析了每种遍历方式的原理与过程。通过具体的二叉树实例演示了遍历算法的应用。

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#include <iostream>
#include <stack>
using namespace std;


struct TreeNode
{
      char val;
      TreeNode *left;
      TreeNode *right;
      TreeNode(char x):val(x),left(NULL),right(NULL)
	  {
	  
	  }
};


//前序
void preorder(TreeNode* root)
{
      if(root==NULL)
           cout<<"The tree is empty!"<<endl;
      stack<TreeNode*> s;
      while(root||!s.empty())
	  {
              while(root)
			  {
                     cout<<root->val<<endl;
                     s.push(root);
                     root=root->left;
              } 
              root=s.top();
              s.pop();
              root=root->right; 
      }
}



//中序
void midorder(TreeNode* root)
{ 
	if(root==NULL)
	{
        cout<<"The tree is empty!"<<endl;	
    }
        stack<TreeNode*> s;
        while(root||!s.empty()){
                while(root){
                s.push(root);
                root=root->left; 
                }
                root=s.top();
                s.pop();
                cout<<root->val;
                root=root->right;
        }

}




void postorder(TreeNode* root){
    if(root==NULL)
        cout<<"empty!"<<endl;
    else{
        stack<TreeNode*> s;
        stack<int> v;
        //跟中序一样，把所以的左子树先放到栈里，这边多了一个标志而已
        while(root)
        {
            s.push(root);
            v.push(0);
            root=root->left;
        }

        while(!s.empty()){
            root=s.top();
            while(root->right&&v.top()==0)  //遍历所以的右子树
             {
                v.pop();
                v.push(1);
                root=root->right;
                s.push(root)
                v.push(0);
                while(root->left)
                {
                     s.push(root);
                     v.push(0);
                     root=root->left;
                }
           }
           root=s.top();
           cout<<root->val;
           s.pop();
           v.pop();
        }
    }
}



int main()
{
		TreeNode G('G');
		TreeNode H('H');
		TreeNode D('D');
		TreeNode B('B');
		TreeNode I('I' );
		TreeNode E('E');
		TreeNode F('F' );
		TreeNode C('C');
		TreeNode A('A');
		A.left = &B;
		A.right = &C;
		B.left = &D;
		D.left = &G;
		D.right = &H;
		C.left = &E;
		C.right = &F;
		E.right = &I;
		//preorder(&A);
		//midorder(&A);
		postorder(&A);
	system("pause");
	return 0;
}