43 递归和非递归俩种方法实现二叉树的三种遍历

/*
43.递归和非递归俩种方法实现二叉树的前序遍历。
*/

#include<iostream>
#include<stdio.h>
#include<stdlib.h>
#include<stack>
#include<queue>  
using namespace std;
#define MAX 20

struct BTreeNode{
  int data;
  BTreeNode *left,*right;
}; 

//建立二叉树 
BTreeNode * CreateTree(int data[],int pos,int len)
{
  BTreeNode *tree;
  if(pos>=len) 
  {
    return NULL;
  }
  else
  {
    tree=(BTreeNode *)malloc(sizeof(BTreeNode));
    tree->data=data[pos];
    tree->left=CreateTree(data,2*pos+1,len);//数组坐标 
    tree->right=CreateTree(data,2*pos+2,len);
    return tree;
  }
  
}

// 递归版本比较简单 
void preOrder(BTreeNode *tree)
{
  if(tree!=NULL)
  {
    printf("%d ",tree->data);
    preOrder(tree->left);
    preOrder(tree->right);
  }
}

void preorderNonrecursive(BTreeNode *tree) 
{
  stack<BTreeNode* > s;
  s.push(tree);
  while(!s.empty()) 
  {
    BTreeNode* n;
    n=s.top();
    s.pop();
    printf("%d ",n->data);//因为是栈，所以先如右边的，后左边的，则先出左边的 
    if(n->right!=NULL) s.push(n->right);
    if(n->left!=NULL) s.push(n->left);    
  }
}


void inorderNonrecursive(BTreeNode* tree) //左根右 
{
  stack<BTreeNode* > s;
  BTreeNode* current=tree;
  
  while(!s.empty()||current!=NULL) 
  {
    if(current!=NULL) 
    {
      s.push(current);// 根先进，在继续左孩子，直到为空 
      current=current->left;
    }
    else 
    {
      current=s.top();
      s.pop();
      printf("%d ",current->data);// 根 
      current=current->right;//右 
    }
  }
}


void postorderNonrecursive(BTreeNode * tree) //左右根 
{
  // visiting occurs only when current has no right child 
  //or last visited is his right child
  stack<BTreeNode *> sTraverse, sVisit;
  sTraverse.push(tree);
  while (!sTraverse.empty()) 
  {
    BTreeNode* p=sTraverse.top();
    sTraverse.pop();
     
    sVisit.push(p);//左右根 根先进 右进 左进
    if (p->left!=NULL) sTraverse.push(p->left); 
    if (p->right!=NULL) sTraverse.push(p->right);
  }
  while(!sVisit.empty()) 
  {
    printf("%d ",sVisit.top()->data);
    sVisit.pop();
  }
}

int main(){
  /*
      8
     6     10
    5   7   9 11
  12 3 1 2 4
  
  前：8 6 5 12 3 7 1 2 10 9 4 11 
  中：12 5 3 6 1 7 2 8 4 9 10 11 
  后：12 3 5 1 2 7 6 4 9 11 10 8 
  */
  int data[]={8,6,10,5,7,9,11,12,3,1,2,4};
  int len=sizeof(data)/sizeof(int);
  
  BTreeNode *tree=CreateTree(data,0,len);

  printf("前序遍历(递归)：\n");//根左右 
  preOrder(tree);printf("\n");
  printf("前序遍历（非递归）：\n");//根左右 
  preorderNonrecursive(tree);printf("\n");
  
  printf("中序遍历（非递归）：\n");//左根右 
  inorderNonrecursive(tree);printf("\n");
  
  printf("后序遍历（非递归）：\n");//左右根 
  postorderNonrecursive(tree);printf("\n");
  
  return 0;
}