C语言实现二叉树遍历的迭代算法

本文实例讲述了C语言实现二叉树遍历的迭代算法，是数据结构算法中非常经典的一类算法。分享给大家供大家参考。

具体实现方法如下：

二叉树中序遍历的迭代算法：

#include <iostream>
#include <stack>

using namespace std;

struct Node {
 Node(int i, Node* l = NULL, Node* r = NULL) : item(i), left(l), right(r) {}
 int item;
 Node* left;
 Node* right;
};

Node* construct() {
 Node* node6 = new Node(16);
 Node* node5 = new Node(12);
 Node* node4 = new Node(8);
 Node* node3 = new Node(4);
 Node* node2 = new Node(14, node5, node6);
 Node* node1 = new Node(6, node3, node4);
 Node* node0 = new Node(10, node1, node2);

 return node0;
}

//递归算法
void inorder(Node *root)
{
 if (root == NULL)
 return;
 inorder(root->left);
 cout << root->item << " ";
 inorder(root->right);
}

void preorder(Node *root)
{
 if(root == NULL)
 return;

 cout << root->item << " ";
 preorder(root->left);
 preorder(root->right);
}

void postorder(Node *root)
{
 if (root == NULL)
 return;

 postorder(root->left);
 postorder(root->right);
 cout << root->item << " ";
}

void postorder2(Node *root)
{
 if (root == NULL)
 return;

 stack<Node *> nstack;
 Node *pre = NULL;
 nstack.push(root);
 Node *node = NULL;

 while (!nstack.empty())
 {
 node = nstack.top();
 if (pre != node->left && pre != node->right)
 {
  if (node->right)
  nstack.push(node->right);
  if (node->left)
  nstack.push(node->left);
 }

 if (node->left == NULL && node->right == NULL
  || pre == node->left || pre == node->right)
 {
  cout << node->item << " ";
  nstack.pop();
 }
 pre = node;
 }
}

void preorder2(Node *root)
{
 if(root == NULL)
 return;

 stack<Node *> nstack;
 Node *node = root;

 while (node != NULL || !nstack.empty())
 {
 while(node != NULL)
 {
  cout << node->item << " ";
  nstack.push(node);
  node = node->left;
 }
 node = nstack.top();
 nstack.pop();
 node = node->right;
 }
}

void preorder3(Node *root)
{
 if (root == NULL)
 return;

 stack<Node *> nstack;
 nstack.push(root);
 Node *node = NULL;

 while (!nstack.empty())
 {
 node = nstack.top();
 nstack.pop();
 cout << node->item << " ";

 if (node->right)
  nstack.push(node->right);
 if (node->left)
  nstack.push(node->left);
 }
}

//迭代算法
void inorder2(Node *root)
{
 if(root == NULL)
 return;

 stack<Node *> nstack;
 nstack.push(root);
 Node *next = root->left;

 while (next != NULL || !nstack.empty())
 {
 while (next != NULL)
 {
  nstack.push(next);
  next = next->left;
 }
 next = nstack.top();
 nstack.pop();

 cout << next->item << " ";
 next = next->right;
 }
}

int main()
{
 Node *root = construct();
 cout << "---------中序遍历递归---------" << endl;
 inorder(root);
 cout << endl;
 cout << "---------中序遍历迭代---------" << endl;
 inorder2(root);
 cout << endl;
 cout << "---------先序遍历递归---------" << endl;
 preorder(root);
 cout << endl;
 cout << "---------先序遍历迭代1---------" << endl;
 preorder2(root);
 cout << endl;
 cout << "---------先序遍历迭代2---------" << endl;
 preorder3(root);
 cout << endl;
 cout << "---------后序遍历递归---------" << endl;
 postorder(root);
 cout << endl;
 cout << "---------后序遍历迭代---------" << endl;
 postorder2(root);
}

关于前序遍历，后来又写的算法如下，供大家参考：

void preOrderIterator(Node *root)
{
 if (root == NULL)
 return;

 stack<Node*> nstack;
 nstack.push(root);

 while (!nstack.empty())
 {
 Node *top = nstack.top();
 while (top != NULL)
 {
  if (top->left)
  nstack.push(top->left);
  cout << top->data << " ";
  top = top->left;
 }
 while (top == NULL && !nstack.empty())
 {
  top = nstack.top()->right;
  nstack.pop();
 }

 if (top != NULL)
  nstack.push(top);
 }
}

相信本文所述对大家C程序算法设计的学习有一定的借鉴价值。