debug skiplist, all tests passed. But I sincerely doubt my coding ability.

thu_dsa/chp3/List.h

@@ -27,8 +27,8 @@ public:
 	//read-only interfaces
 	ListNodePosi(T) first() const { return head->succ; }
 	ListNodePosi(T) last() const { return tail->prev; }
-	ListNodePosi(T) prev(ListNodePosi(T) p) const { return p->prev; }
-	ListNodePosi(T) next(ListNodePosi(T) p) const { return p->next; }
+	ListNodePosi(T) prev(ListNodePosi(T) p) const { return p->prev == head? nullptr: p->prev; }
+	ListNodePosi(T) next(ListNodePosi(T) p) const { return p->succ == tail? nullptr: p->succ; }
 	ListNodePosi(T) find(T const &val) const { return find(val, size, tail); }		//find val from all elements of the list
 	ListNodePosi(T) find(T const &val, int n, ListNodePosi(T) p) const;				//find val from a range of n elements before p
 	ListNodePosi(T) search(T const &val, int n, ListNodePosi(T) p) const;			//find val in a sorted List<T>

thu_dsa/chp9/dict.h

@@ -5,7 +5,7 @@
 template <typename K, typename V>
 class Dict{
 public:
-	virtual int  size() = 0;
+	virtual int  size() const = 0;
 	virtual V    get(K key) = 0;
 	virtual bool put(K key, V value) = 0;
 	virtual bool remove(K key) = 0;

thu_dsa/chp9/quadlist.h

@@ -29,20 +29,20 @@ public:
 	//constructor
 	QuadList();
 
-	//deconstrutor
-	~QuadList();
-
 	//external interfaces
 
 	//read-only interfaces
 	int  size()  const { return __size; }
 	bool empty() const { return size() == 0; }
-	QuadNodePosi(T) first() const { return empty()? nullptr : __head->next;}
-	QuadNodePosi(T) last()  const { return empty()? nullptr : __tail->prev;}
+	QuadNodePosi(T) first() const { return __head->next;}
+	QuadNodePosi(T) last()  const { return __tail->prev;}
 	QuadNodePosi(T) prev(QuadNodePosi(T) p)  const { return p->prev; }
 	QuadNodePosi(T) next(QuadNodePosi(T) p)  const { return p->next; }
 
 	//writable interfaces
+	void sethead(T entry) { __head->entry = entry; }
+	void settail(T entry) { __tail->entry = entry; }
+	void connectTo(QuadList<T>* down);
 	void insert_before_above(QuadNodePosi(T) p, T const& entry, QuadNodePosi(T) base = nullptr);
 	void insert_after_above(QuadNodePosi(T)p, T const & entry, QuadNodePosi(T) base = nullptr);
 	void remove(QuadNodePosi(T) p);
@@ -51,15 +51,26 @@ public:
 //constructor
 template <typename T>
 QuadList<T>::QuadList(){
-	__head = new QuadNode<T>(MININT);
-	__tail = new QuadNode<T>(MAXINT);
+	__head = new QuadNode<T>();
+	__tail = new QuadNode<T>();
 	__size = 0;
 	__head->next = __tail;
+	__head->prev = __tail;
+	__tail->next = __head;
 	__tail->prev = __head;
 }
 
 //writable interfaces
 
+template <typename T>
+void QuadList<T>::connectTo(QuadList<T>* down){
+	//assert(down != nullptr);
+	__head->below = down->__head;
+	__tail->below = down->__tail;
+	down->__head->above = __head;
+	down->__tail->above = __tail;
+}
+
 template <typename T>
 void QuadList<T>::insert_before_above(QuadNodePosi(T) p, T const & entry, QuadNodePosi(T) base){
 	QuadNodePosi(T) newNode = new QuadNode<T>(entry);
@@ -67,7 +78,7 @@ void QuadList<T>::insert_before_above(QuadNodePosi(T) p, T const & entry, QuadNo
 	newNode->prev = p->prev;
 	p->prev = newNode;
 	newNode->prev->next = newNode;
-	base->above = newNode;
+	if(base) base->above = newNode;
 	newNode->below = base;
 	++__size;
 }

thu_dsa/chp9/skiplist.h

@@ -5,6 +5,7 @@
 #include "quadlist.h"
 #include "../chp3/List.h"
 #include <iostream>
+#include <iomanip>
 #include <cstdlib>
 #include <ctime>
 
@@ -20,7 +21,7 @@ public:
 	entry() = default;
 	entry(K key, V value) : key(key), value(value) {}
 
-	operator==(entry const &e){
+	bool operator==(entry const &e){
 		return key == e.key;
 	}
 };
@@ -34,18 +35,21 @@ public:
 	//constructor
 	SkipList();
 
-	int  size()  const { return first()->size(); }
+	int  size()  const { return first()->val->size(); }
 	int  level() const { return getSize(); }
 
 	V    get(K key);
 	bool put(K key, V value);
 	bool remove(K key);
+	void print() const;
 };
 
 //constructor
 template <typename K, typename V>
 SkipList<K, V>::SkipList(){
 	QuadList<entry<K, V>>* qlist = new QuadList<entry<K, V>>();
+	qlist->sethead(entry<K, V>(MININT, 0));
+	qlist->settail(entry<K, V>(MAXINT, 0));
 	push_back(qlist);
 }
 
@@ -53,8 +57,8 @@ SkipList<K, V>::SkipList(){
 
 template <typename K, typename V>
 QuadNode<entry<K, V>>* SkipList<K, V>::skipSearch(K key) {
-	while (1) {
-		QuadNode<entry<K, V>>* qnode = last()->first();					//the first quadlist node of the last quadlist
+	QuadNode<entry<K, V>>* qnode = last()->val->first();			//the first quadlist node of the last quadlist
+	while (1) {	
 		while (qnode->entry.key < key) qnode = qnode->next;
 		if (qnode->entry.key == key) return qnode;
 		//else
@@ -81,22 +85,33 @@ template <typename K, typename V>
 bool SkipList<K, V>::put(K key, V value){
 	QuadNode<entry<K, V>>* qnode = skipSearch(key);
 	QuadNode<entry<K, V>>* belowNode;
-	ListNode<QuadList<entry<K, V>>*>* qlist = first();
+	ListNode<QuadList<entry<K, V>>*> *qlist = first();
+	QuadList<entry<K, V>> *newlist;
 
 	while (qnode->below != nullptr) qnode = qnode->below;
 	if (qnode->entry.key != key) qnode = qnode->next;
 	qlist->val->insert_before_above(qnode, entry<K, V>(key, value));
+	if (next(qlist) == nullptr) {
+		newlist = new QuadList<entry<K, V>>();
+		newlist->sethead(entry<K, V>(MININT, 0));
+		newlist->settail(entry<K, V>(MAXINT, 0));
+		newlist->connectTo(qlist->val);
+		push_back(newlist);
+	}
 
-	srand((int)time(0));
-	while(rand() & 1){
+	while(rand() % 2 == 0){
 		belowNode = qnode->prev;
 		qlist = next(qlist);
-		if(qlist->val->empty()){
-			push_back(new QuadList<entry<K, V>>());
-		}
 		while (qnode->above == nullptr) qnode = qnode->next;
 		qnode = qnode->above;
 		qlist->val->insert_before_above(qnode, entry<K, V>(key, value), belowNode);
+		if (next(qlist) == nullptr) {
+			newlist = new QuadList<entry<K, V>>();
+			newlist->sethead(entry<K, V>(MININT, 0));
+			newlist->settail(entry<K, V>(MAXINT, 0));
+			newlist->connectTo(qlist->val);
+			push_back(newlist);
+		}
 	}
 	return true;
 }
@@ -114,10 +129,44 @@ bool SkipList<K, V>::remove(K key){
 		tempNode = qnode;
 		qlist->val->remove(qnode);
 		qnode = qnode->above;
-		qlist = qlist->val->next();
+		qlist = next(qlist);
 		delete tempNode;
 	}
+
+	//remove level if empty
+	qlist = prev(last());
+	while(qlist && qlist->val->empty()){
+		pop_back();
+		qlist = prev(qlist);
+	}
+
 	return true;
 }
 
+template <typename K, typename V>
+void SkipList<K, V>::print() const{
+	QuadList<entry<K, V>>* qlist = first()->val;
+	QuadNode<entry<K, V>>* qnode;
+	QuadNode<entry<K, V>>* tempNode;
+	int* currLevel = new int[size()], idx = 0;
+	for(qnode = qlist->first(); qnode->entry.key != MAXINT; qnode = qnode->next){
+		currLevel[idx] = 0;
+		tempNode = qnode;
+		while(tempNode){
+			currLevel[idx]++;
+			tempNode = tempNode->above;
+		}
+		++idx;
+	}
+
+	for (int jx = level(); jx != 0; --jx) {
+		idx = 0;
+		for (qnode = qlist->first(); qnode->entry.key != MAXINT; qnode = qnode->next){
+			if (currLevel[idx++] >= jx) cout << qnode->entry.key << '\t';
+			else                        cout << " " << '\t';
+		}
+		cout << endl;
+	}
+}
+
 #endif

thu_dsa/chp9/test_skiplist.cpp

@@ -0,0 +1,52 @@
+#include "skiplist.h"
+#include <iostream>
+#include <cassert>
+
+using std::cout;
+using std::endl;
+
+void basic_test();
+void insert_delete_test();
+
+int main(){
+	cout << "begin tests ..." << endl;
+
+	basic_test();
+	insert_delete_test();
+	
+	cout << "All tests passed." << endl;
+	system("pause");
+	return 0;
+}
+
+void basic_test(){
+	SkipList<int, int> slist;
+	assert(slist.size() == 0);
+	assert(slist.level() == 1);
+	slist.print();
+
+	assert(slist.remove(0) == false);
+
+	cout << "basic_test passed." << endl;
+}
+
+void insert_delete_test(){
+	SkipList<int, int> slist;
+	int src[15] = { 5, 9, 0, 2, 3, 6, 1, 7, 4, 8, 3, 8, 4, 7, 7 };
+	srand((unsigned int)time(0));
+	for (int ix = 0; ix != 15; ++ix) {
+		slist.put(src[ix], src[ix]);
+		cout << "This is the " << ix + 1 << "th insert, the level is " << slist.level() << endl;
+		slist.print();
+	}
+
+	cout << endl;
+
+	for(int ix = 0; ix != 15; ++ix){
+		slist.remove(src[ix]);
+		cout << "This is the " << ix + 1 << "th delete, the level is " << slist.level() << endl;
+		slist.print();
+	}
+
+	cout << "insert_delete test passed." << endl;
+}