二叉树的线索化（2种实现方式）

1.全局变量

typedef struct ThreadNode {
	ELemType data;
	struct ThreadNode *lchild, *rchild;
	int ltag, rtag;
}ThreadNode, *ThreadTree;

ThreadNode *pre = NULL;

1.1中序线索化

void CreateInThread(ThreadTree T) {
	pre = NULL;
	if(T !== NULL) {
		InThread(T);
		if(pre -> rchild == NULL)
			pre -> rtag = 1;
	}
}

void InThread(ThreadTree T) {
	if(T != NULL) {
		InTread(T -> lchild);
		visit(T);
		InTread(T -> rchild);
	}
}

void visit(ThreadNode *q) {
	if(q -> lchild == NULL) {
		q -> lchild = pre;
		q -> ltag = 1;
	}
	if(pre != NULL&& pre -> rchild == NULL) {
		pre -> rchild = q;
		pre -> rlog = 1;
	}
	pre = q;
}

1.2先序线索化

void CreatePreThread(ThreadTree T) {
	pre = NULL;
	if(T !== NULL) {
		PreThread(T);
		if(pre -> rchild == NULL)
			pre -> rtag = 1;
	}
}

void InThread(ThreadTree T) {
	if(T != NULL) {
		visit(T);
		if(T -> ltag == 0)
			PreThread(T -> lchild);//解决先序线索化转圈问题
		PreThread(T -> rchild);
	}
}

void visit(ThreadNode *q) {
	if(q -> lchild == NULL) {
		q -> lchild = pre;
		q -> ltag = 1;
	}
	if(pre != NULL&& pre -> rchild == NULL) {
		pre -> rchild = q;
		pre -> rlog = 1;
	}
	pre = q;
}

1.3后序线索化

void CreatePostThread(ThreadTree T) {
	pre = NULL;
	if(T !== NULL) {
		PostThread(T);
		if(pre -> rchild == NULL)
			pre -> rtag = 1;
	}
}

void InThread(ThreadTree T) {
	if(T != NULL) {
		PostThread(T -> lchild);
		PostThread(T -> rchild);
		visit(T);
	}
}

void visit(ThreadNode *q) {
	if(q -> lchild == NULL) {
		q -> lchild = pre;
		q -> ltag = 1;
	}
	if(pre != NULL&& pre -> rchild == NULL) {
		pre -> rchild = q;
		pre -> rlog = 1;
	}
	pre = q;
}

2.引用

typedef struct ThreadNode {
	ELemType data;
	struct ThreadNode *lchild, *rchild;
	int ltag, rtag;
}ThreadNode, *ThreadTree;

2.1中序线索化

void CreateInThread(ThreadTree T) {
	ThreadTree pre = NULL;
	if(T != NULL) {
		InThread(T,pre);
		pre -> rchild = NULL;
		pre -> rtag = 1;
	}
}

void InThread(ThreadTree &p, ThreadTree &pre) {
	if(p != NULL) {
		InThread(p -> lchild, pre);
		if(p -> lchild == NULL){
			p -> lchild == pre;
			p -> ltag == 1;
		}
		if(pre != NULL && pre -> rchild == NULL) {
			pre -> rchild = p;
			pre -> rtag = 1;
		}
		pre = p;
		InThread(p -> rchild, pre);
	}
}

2.2先序线索化

void CreatePreThread(ThreadTree T) {
	ThreadTree pre = NULL;
	if(T != NULL) {
		PreThread(T,pre);
		pre -> rchild = NULL;
		pre -> rtag = 1;
	}
}

void PreThread(ThreadTree &p, ThreadTree &pre) {
	if(p != NULL) {
		if(p -> lchild == NULL){
			p -> lchild == pre;
			p -> ltag == 1;
		}
		if(pre != NULL && pre -> rchild == NULL) {
			pre -> rchild = p;
			pre -> rtag = 1;
		}
		pre = p;
		if(T -> ltag == 0)
			PreThread(p -> lchild, pre);
		PreThread(p -> rchild, pre);
	}
}

2.3后序线索化

void CreatePostThread(ThreadTree T) {
	ThreadTree pre = NULL;
	if(T != NULL) {
		PostThread(T,pre);
		pre -> rchild = NULL;
		pre -> rtag = 1;
	}
}

void PostThread(ThreadTree &p, ThreadTree &pre) {
	if(p != NULL) {
		PostThread(p -> lchild, pre);
		PostThread(p -> rchild, pre);
		if(p -> lchild == NULL){
			p -> lchild == pre;
			p -> ltag == 1;
		}
		if(pre != NULL && pre -> rchild == NULL) {
			pre -> rchild = p;
			pre -> rtag = 1;
		}
		pre = p;
	}
}