【0】README 0.1）本代碼均為原創，旨在將樹的遍歷應用一下下以加深印象而已；（回答了學習樹的遍歷到底有什么用的問題？）你對比下linux 中的文件樹 和我的打印結果就明理了；
0.2）我們采用的是 兒子兄弟表示法 來 表示樹的整體節點構造； 0.3）兒子兄弟表示法介紹 0.3.1）如下圖所示：?向下的箭頭（左指針）指向第一個兒子節點， 從左到右的箭頭（右指針）指向下一個兄弟節點；（間接說明了樹的節點有兩個指針） 0.3.2）樹節點定義代碼如下： struct Tree; typedef struct Tree *Tree;// we adopt child-sibling notation struct Tree {ElementType value;Tree firstChild;Tree nextSibling; }; 0.4）哥子第一次 使用著 丑到逼爆 的 編輯器，也是醉了，主要是markdown 對于源代碼文件顯示不夠清晰， oh m g；
【1】任務來了 我們想要列出目錄中所有文件的名字，?我們的輸出格式將是：深度為 depth 的文件的名字將被?depth?次跳格縮進后打印出來； 【2】給出先序遍歷+后序遍歷目錄樹的實現代碼 2.1）先序遍歷步驟： step1）訪問根節點； step2）先序遍歷以兒子為根的子樹； step3）先序遍歷以兄弟為根的子樹； download source code：https://github.com/pacosonTang/dataStructure-algorithmAnalysis/blob/master/chapter4/p68_preorder_common_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 preorder traversal. void printPreorder(int depth, Tree root) { int i;if(root) { for(i = 0; i < depth; i++)printf(" ");printf("%c\n", root->value); printPreorder(depth + 1, root->firstChild); printPreorder(depth, root->nextSibling);} }int main() {Tree tree;tree = createTree();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));printPreorder(1, tree);printf("\n test for insert 'E' 'F' into the parent '/' \n"); insert('E', find('/', tree));insert('F', find('/', tree));printPreorder(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));printPreorder(1, tree);return 0; }
打印結果如下：


2.2）后序遍歷步驟：（不同于二叉樹的后序）
step1）后序遍歷以兒子為根的子樹；
step2）訪問根節點； step3）后序遍歷以兄弟為根的子樹； 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; }
打印結果如下：

總結

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