王道数据结构 （10） 树的先序遍历非递归代码实现

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#define ElementType char
int top = -1; //定义top栈顶元素下标

// 结点结构体
typedef struct BinTNode
{
  ElementType data;
  struct BinTNode *left;
  struct BinTNode *right;
} BinTNode, *BinTree;

// 初始化树形结构
BinTNode *CreateBiTree(BinTNode *T)
{
  T = (BinTNode *)malloc(sizeof(BinTNode));
  T->data = ‘A‘;
  T->left = (BinTNode *)malloc(sizeof(BinTNode));
  T->left->data = ‘B‘;
  T->right = (BinTNode *)malloc(sizeof(BinTNode));
  T->right->data = ‘C‘;

  T->left->left = (BinTNode *)malloc(sizeof(BinTNode));
  T->left->left->data = ‘D‘;
  T->left->right = (BinTNode *)malloc(sizeof(BinTNode));
  T->left->right->data = ‘E‘;
  T->left->right->left = NULL;
  T->left->right->right = NULL;
  T->left->left->left = (BinTNode *)malloc(sizeof(BinTNode));
  T->left->left->left->data = ‘H‘;
  T->left->left->left->left = NULL;
  T->left->left->left->right = NULL;
  T->left->left->right = (BinTNode *)malloc(sizeof(BinTNode));
  T->left->left->right->data = ‘I‘;
  T->left->left->right->left = NULL;
  T->left->left->right->right = NULL;

  T->right->left = (BinTNode *)malloc(sizeof(BinTNode));
  T->right->left->data = ‘F‘;
  T->right->left->left = NULL;
  T->right->left->right = NULL;
  T->right->right = (BinTNode *)malloc(sizeof(BinTNode));
  T->right->right->data = ‘G‘;
  T->right->right->left = NULL;
  T->right->right->right = NULL;

  return T;
}

// 栈 - 进栈push
void push(BinTNode **stack, BinTNode *elem)
{
  stack[++top] = elem;
}

//栈 - 弹栈pop
void pop()
{
  if (top == -1)
  {
    return;
  }
  top--;
}

// 遍历过程中，输出结点值
void printElement(BinTNode *elem)
{
  printf("%c ", elem->data);
}

//获取栈顶元素
BinTNode *getTop(BinTNode **stack)
{
  return stack[top];
}

//非递归遍历 - 左根右
void InOrderTraverse(BinTNode *Tree)
{
  BinTNode *stack[20]; // 定义一个栈
  BinTNode *p = Tree;  // 定义临时指针
  // 1 当前指针指向不为NULL - 说明有右孩子
  // 2 或者栈内不空 - 说明该指针处没有右孩子，继续弹出结点值
  while (p || top != -1)
  {
    while (p)
    {
      printElement(p);
      push(stack, p); // 循环将左孩子进栈
      p = p->left;
    }
    if (top != -1)
    {
      p = getTop(stack); //取栈顶元素
      pop();             //栈顶元素弹栈
      p = p->right;
    }
  }
}

int main()
{
  BinTNode *Tree;
  Tree = CreateBiTree(Tree);
  printf("先序遍历:\t");
  InOrderTraverse(Tree);
  printf("\n");
  return 0;
}