二叉树的前序、中序、后序遍历（非递归）

一、前中后序的非递归遍历

 代码中采用先序遍历的方法创建二叉树，示例创建二叉树格式如下：

创建过程中，以表示空节点。

代码：

#include <stdio.h>#include <stdlib.h>typedef struct BTNode{    char data;    struct BTNode *left;    struct BTNode *right;}BTNode,*BTree;typedef struct Stack{    BTree data[101];    int top;}BTStack;typedef struct Post_BTNode{    BTNode * Post_Node;    int tag;}Post_BTNode,*Post_BTree;typedef struct Post_Stack{    Post_BTNode data[101];    int top;}Post_Stack;BTree CreatBTree(BTree root)//先序构建二叉树{   char data;   scanf("%c",&data);   getchar();   if(data == '*')        root = NULL;   else{        root = (BTree)malloc(sizeof(BTNode));        root->data = data;        root->left = CreatBTree(root->left);        root->right = CreatBTree(root->right);   }   return root;}void PreOrder_NonRec(BTree root)//先序遍历非递归{    BTStack stack;    stack.top = -1;    BTNode *p=NULL;    if(NULL != root)    {        stack.data[++stack.top] = root;        while(stack.top > -1)        {            p = stack.data[stack.top--];            printf(" %c",p->data);            if(NULL != p->right)                stack.data[++stack.top] = p->right;            if(NULL != p->left)                stack.data[++stack.top] = p->left;        }    }    printf("\n");}void Inorder_NonRec(BTree root)//中序遍历非递归{    BTStack stack;    BTNode *p = NULL;    stack.top = -1;    p = root;    while(NULL != p || stack.top > -1)    {        while(NULL != p)        {            stack.data[++stack.top]=p;            p = p->left;        }        p = stack.data[stack.top--];        printf(" %c",p->data);        p = p->right;    }    printf("\n");}void PostOrder_NonRec(BTree root)//后续遍历非递归{    Post_Stack stack;    Post_BTNode node;    BTNode * p=NULL;    p= root;    stack.top = -1;    while(NULL != p || stack.top > -1)    {        while(NULL != p)        {            node.Post_Node=p;            node.tag = 1;            stack.data[++stack.top] = node;            p = p->left;        }        node = stack.data[stack.top--];        if(node.tag == 1)        {            node.tag = 2;            stack.data[++stack.top] = node;            p = node.Post_Node->right;        }        else if(node.tag == 2)        {            p = node.Post_Node;            printf(" %c",p->data);            p = NULL;        }    }    printf("\n");}int main(){    BTree root=NULL;    root = CreatBTree(root);    printf("PreOrder:");    PreOrder_NonRec(root);    printf("InOrder:");    Inorder_NonRec(root);    printf("PostOrder:");    PostOrder_NonRec(root);    return 0;}

运行结果：

二、根据前序和中序求后序

直接上代码（有注释）：

#include <stdio.h>#include <string.h>void preInToPost(char * pre,char * in, int size){    if(size == 0)    {        return ;    }    char ch = *(pre+0);  //当前子树的根节点    int rootIndex = 0;  //查找当前子树的根节点在中序遍历中的位置    for(;rootIndex<size;rootIndex++)    {        if(ch == *(in+rootIndex))        break;    }    preInToPost(pre+1,in,rootIndex); //递归根据左子树的前序和中序求后序    preInToPost(pre+rootIndex+1,in+rootIndex+1,size-(rootIndex+1)); //递归根据右子树的前序中序求后序    printf("%c",ch); //因为是后序序列，所以在左右子树输出完后输出当前根节点}int main(){    char * preOrder = "abchdefg"; //前序序列    char * inOrder  = "hcbdafeg"; //中序序列    int size = strlen(preOrder);    printf("前序序列：%s\n",preOrder);    printf("中序序列：%s\n",inOrder);    printf("后序序列：");    preInToPost(preOrder,inOrder,size);    return 0;}

结果：