【学习笔记】非递归实现先后根遍历二叉树
C语言代码:
1 #include <stdio.h> 2 #include <string.h> 3 #include <stdlib.h> 4 5 /*----方便看代码的定义----*/ 6 typedef int Status; 7 #define OK 0 8 #define NotOK 1 9 10 #define STACK_INIT_SIZE 100 //栈空间初始分配量 11 #define STACKINCREMENT 10 //栈空间分配增量 12 /*------------------------*/ 13 14 /*-----定义树结构-----*/ 15 typedef struct BiTree{ 16 char data; 17 struct BiTree *Lchild; 18 struct BiTree *Rchild; 19 }BiTree,*TreeNode; 20 /*--------------------*/ 21 22 /*-----输入字符串形式建立树(基于先根)-----*/ 23 /*例：输入 ABD#E##F##CG##HI### 24 将会生成： A 25 / \ 26 B C 27 / \ / \ 28 D F G H 29 \ / 30 E I */ 31 TreeNode CreateBiTree(){ 32 char ch; 33 TreeNode T; 34 scanf("%c",&ch); 35 if( ch == '#' ){ 36 T=NULL; 37 } 38 else{ 39 T = (TreeNode)malloc(sizeof(BiTree)); 40 T->data = ch; 41 T->Lchild = CreateBiTree(); 42 T->Rchild = CreateBiTree(); 43 } 44 return T; 45 } 46 /*-----------------------------------------*/ 47 48 /*------------------------建立栈------------------------*/ 49 typedef struct{ 50 TreeNode *base; //在栈构造之前和销毁之后，base的值为NULL 51 TreeNode *top; //栈顶指针 52 int stacksize; //当前已分配的存储空间，以元素为单位 53 }Stack; 54 55 Status InitStack(Stack &S){ 56 //构造一个空栈S 57 S.base = (TreeNode *)malloc(STACK_INIT_SIZE * sizeof(TreeNode)); 58 if(!S.base){ 59 exit(NotOK); //存储分配失败 60 } 61 S.top = S.base; 62 S.stacksize = STACK_INIT_SIZE; 63 return OK; 64 } 65 66 Status GetTop(Stack S, TreeNode &e){ 67 //若栈不空，则用e返回S的栈顶元素，并返回OK；否则返回NotOK 68 if(S.top == S.base){ 69 return NotOK; 70 } 71 e = *(S.top-1); 72 return OK; 73 } 74 75 Status Push(Stack &S, TreeNode e){ 76 //插入元素e为新的栈顶元素 77 if(S.top - S.base >= S.stacksize){ 78 //栈满，追加存储空间 79 S.base = (TreeNode *)realloc(S.base, (S.stacksize + STACKINCREMENT)*sizeof(TreeNode)); 80 if(!S.base){ 81 //存储分配失败 82 exit(NotOK); 83 } 84 S.top = S.base + S.stacksize; 85 S.stacksize += STACKINCREMENT; 86 } 87 *S.top++ = e; 88 return OK; 89 } 90 91 Status Pop(Stack &S, TreeNode &e){ 92 //若栈不空，则删除S的栈顶元素，用e返回其值，并返回OK；否则返回NotOK 93 if(S.top == S.base){ 94 return NotOK; 95 } 96 e = * --S.top; 97 return OK; 98 } 99 100 bool StackIsEmpty(Stack &S){ 101 //若栈为空，返回true；若栈非空，返回false 102 if(S.top == S.base){ 103 return true; 104 } 105 else{ 106 return false; 107 } 108 } 109 /*------------------------------------------------------*/ 110 111 /*------非递归先根遍历------*/ 112 Status PreOrderTraverse(TreeNode T){ 113 if( T == NULL ){ 114 return NotOK; 115 } 116 else{ 117 printf("PreOrderTraverse:"); 118 Stack TreeStack; 119 InitStack(TreeStack); 120 while( T!=NULL || !StackIsEmpty(TreeStack)){ 121 while(T != NULL){ 122 printf("%c",T->data); 123 Push(TreeStack,T); 124 T = T->Lchild; 125 } 126 if(!StackIsEmpty(TreeStack)){ 127 Pop(TreeStack,T); 128 T = T->Rchild; 129 } 130 } 131 printf("\n"); 132 return OK; 133 } 134 } 135 /*--------------------------*/ 136 137 /*------非递归后根遍历------*/ 138 Status PostOrderTraverse(TreeNode T){ 139 if( T == NULL ){ 140 return NotOK; 141 } 142 else{ 143 printf("PostOrderTraverse:"); 144 Stack TreeStack; 145 TreeNode last; 146 TreeNode current; 147 Push(TreeStack,T); 148 while(!StackIsEmpty(TreeStack)){ 149 GetTop(TreeStack,current); 150 if((current->Lchild==NULL && current->Rchild==NULL) 151 || (last != NULL && (last == current->Lchild 152 || last == current->Rchild))){ 153 printf("%c",current->data); 154 Pop(TreeStack, last); 155 } 156 else{ 157 if(current->Rchild != NULL){ 158 Push(TreeStack,current->Rchild); 159 } 160 if(current->Lchild != NULL){ 161 Push(TreeStack,current->Lchild); 162 } 163 } 164 } 165 printf("\n"); 166 return OK; 167 } 168 } 169 /*--------------------------*/ 170 171 /*-----主函数-----*/ 172 int main(){ 173 TreeNode TreeRoot; 174 TreeRoot = CreateBiTree(); 175 PreOrderTraverse(TreeRoot); 176 PostOrderTraverse(TreeRoot); 177 } 178 /*----------------*/
运行结果:
