0.2）我们采用的是 儿子兄弟表示法 来 表示树的整体节点构造；

0.3）儿子兄弟表示法介绍

struct Tree;
typedef struct Tree *Tree;// we adopt child-sibling notation
struct Tree
{ElementType value;Tree firstChild;Tree nextSibling;
};

2.2）后序遍历步骤：（不同于二叉树的后序）

step1）后序遍历以儿子为根的子树；

step2）访问根节点；

step3）后序遍历以兄弟为根的子树；

download source code：https://github.com/pacosonTang/dataStructure-algorithmAnalysis/blob/master/chapter4/p69_postorder_commone_tree.c

source code at a glance:

#include <stdio.h>
#include <malloc.h>#define ElementType char
#define Error(str) printf("\n error: %s \n",str)   struct Tree;
typedef struct Tree *Tree;Tree createTree();
Tree makeEmpty(Tree t);
Tree insert(ElementType e, Tree t);// we adopt child-sibling notation
struct Tree
{ElementType value;Tree firstChild;Tree nextSibling;
};// create a tree with root node
Tree createTree()
{   Tree t;t = (Tree)malloc(sizeof(struct Tree));if(!t) {Error("out of space, from func createTree");        return NULL;}    t->firstChild = NULL;t->nextSibling = NULL;    t->value = '/';return t;
}// make the tree empty
Tree makeEmpty(Tree t)
{if(t){makeEmpty(t->firstChild);makeEmpty(t->nextSibling);        free(t);}           return NULL;
}//
Tree insert(ElementType e, Tree parent)
{Tree child;Tree newSibling;if(!parent){Error("for parent tree node is empty , you cannot insert one into the parent node, from func insert");        return NULL;}newSibling = (Tree)malloc(sizeof(struct Tree));if(!newSibling) {Error("out of space, from func insert");        return NULL;}newSibling->value = e;newSibling->nextSibling = NULL;newSibling->firstChild = NULL;// building the node with value e overchild = parent->firstChild;   if(!child) {parent->firstChild = newSibling;return parent;}while(child->nextSibling)child = child->nextSibling; // find the last child of parent nodechild->nextSibling = newSibling;return parent;
}// find the tree root node with value equaling to e
Tree find(ElementType e, Tree root)
{Tree temp;if(root == NULL)return NULL;if(root->value == e)return root;temp = find(e, root->firstChild); if(temp) return temp;elsereturn     find(e, root->nextSibling);
}// analog print directories and files name in the tree, which involves postorder traversal.
void printPostorder(int depth, Tree root)
{           int i;if(root) {                        printPostorder(depth + 1, root->firstChild);                                            for(i = 0; i < depth; i++)printf("    ");       printf("%c\n", root->value);           printPostorder(depth, root->nextSibling);}
}int main()
{Tree tree;tree = createTree();printf("\n ====== test for postordering the common tree presented by child_sibling structure  ====== \n");    printf("\n test for insert 'A' 'B' into the parent '/' and 'C' 'D' into the parent 'A' \n");  insert('A', tree);    insert('B', find('/', tree));   insert('C', find('A', tree));insert('D', find('A', tree));printPostorder(1, tree);printf("\n test for insert 'E' 'F' into the parent '/'  \n"); insert('E', find('/', tree));insert('F', find('/', tree));printPostorder(1, tree);printf("\n test for insert 'G' 'H' into the parent 'E' and 'I' into the parent 'H' and even 'J' 'K' into the parent 'I' \n");   insert('G', find('E', tree));insert('H', find('E', tree));insert('I', find('H', tree));insert('J', find('I', tree));insert('K', find('I', tree));printPostorder(1, tree);return 0;
} 

打印结果如下：