该B树Java代码实现完全由本人纯手打。
该代码的实现参照了《算法导论》中的伪代码实现思路。
欢迎大家指出问题。
代码：
package datastructure;
//由于本人技术辣鸡，无法实现泛型数组，暂且用Integer替代
//因为没有了解到插入时 k == key 的情况是什么概念，故假设插入时没有 k == key 的情况
public class BTree {
private final static int T = 3;
private final void READ(Entry e) {
System.out.println("Read");
}
private final void WRITE(Entry e) {
System.out.println("Write");
}
private final Entry ALLOCATE() {
return new Entry();
}
private final void CLEAR(Entry e) {
System.out.println("Clear");
}
private class Entry {
public Integer[] key;
public Entry[] child;
public int num;
public boolean leaf;
public Entry() {
key = new Integer[2 * T];
child = new Entry[2 * T + 1];
num = 0;
leaf = false;
}
}
private class EntryPosition {
public Entry entry;
public int position;
public EntryPosition(Entry entry, int position) {
this.entry = entry;
this.position = position;
}
}
Entry root;
public BTree() {
root = ALLOCATE();
root.leaf = true;
}
public EntryPosition search(Integer k) {
return doSearch(k);
}
private EntryPosition doSearch(Integer k) {
Entry e = root;
while (true) {
int i = 1;
while (i <= e.num && k < e.key[i]) {
i++;
}
if (k == e.key[i]) {
return new EntryPosition(e, i);
} else if (i > e.num && e.leaf) {
return null;
} else {
READ(e.child[i]);
e = e.child[i];
}
}
}
public void insert(Integer k) {
doInsert(k);
}
private void doInsert(Integer k) {
Entry e = root;
if (e.num == 2 * T - 1) {
Entry entry = ALLOCATE();
root = entry;
entry.child[1] = e;
doSplit(entry, 1);
doInsertNotFull(entry, k);
} else {
doInsertNotFull(e, k);
}
}
private void doInsertNotFull(Entry e, Integer k) {
while (true) {
int i = 1;
while (i <= e.num && k > e.key[i]) {
i++;
}
if (e.leaf) {
for (int j = e.num; j >= i; j--) {
e.key[j + 1] = e.key[j];
}
e.key[i] = k;
e.num++;
WRITE(e);
System.out.println("insert complete!");
return;
} else {
READ(e.child[i]);
if (e.child[i].num == 2 * T - 1) {
doSplit(e, i);
if (k > e.key[i]) {
i++;
}
}
e = e.child[i];
}
}
}
private void doSplit(Entry e, int i) {
Entry eLeft = e.child[i];
Entry eRight = ALLOCATE();
eRight.leaf = eLeft.leaf;
for (int j = 1; j < T; j++) {
eRight.key[j] = eLeft.key[j + T];
}
for (int j = 1; j <= T; j++) {
eRight.child[j] = eLeft.child[j + T];
}
eRight.num = T - 1;
eLeft.num = T - 1;
for (int j = e.num; j >= i; j--) {
e.key[j + 1] = e.key[j];
}
e.key[i] = eLeft.key[T];
for (int j = e.num + 1; j >= i + 1; j--) {
e.child[j + 1] = e.child[j];
}
e.child[i + 1] = eRight;
e.num++;
WRITE(e);
WRITE(eLeft);
WRITE(eRight);
}
public void delete(Integer k) {
doDeleteStart(k);
}
private void doDeleteStart(Integer k) {
Entry e = root;
if (e.num == 0) {
return;
}
doDelete(e, k);
if (e.num == 0) {
System.out.println("high down");
READ(e.child[1]);
root = e.child[1];
}
CLEAR(e);
System.out.println("Delete complete");
}
private void doDelete(Entry e, Integer k) {
System.out.println("start delete");
while (true) {
int i = 1;
while (i <= e.num && k > e.key[i]) {
i++;
}
if(e.leaf && k != e.key[i]){
return ;
}
EntryPosition epn = new EntryPosition(e, i);
if (i <= e.num && k == e.key[i]) {
if (e.leaf) {// 1
System.out.println("delete leaf");
for (int j = i; j <= e.num - 1; j++) {
e.key[j] = e.key[j + 1];
}
e.num--;
return ;
} else {// 2
READ(e.child[i]);
if (e.child[i].num >= T) {// 2a
EntryPosition ep = getPrecuesor(epn);
e.key[i] = k = ep.entry.key[ep.position];
e = ep.entry;
} else {
READ(e.child[i + 1]);
if (e.child[i + 1].num >= T) {// 2b
EntryPosition ep = getSubsequent(epn);
e.key[i] = k = ep.entry.key[ep.position];
e = ep.entry;
} else {// 2c
Entry y = e.child[i];
Entry z = e.child[i + 1];
y.key[T] = e.key[i];
for (int j = 1; j <= T - 1; j++) {
y.key[T + j] = z.key[j];
}
for (int j = 1; j <= T; j++) {
y.child[T + j] = z.child[j];
}
for (int j = i; j <= e.num - 1; j++) {
e.key[j] = e.key[j + 1];
}
for (int j = i + 1; j <= e.num; j++) {
e.child[j] = e.child[j + 1];
}
e.num--;
y.num = 2 * T - 1;
e = y;
CLEAR(z);
}
}
}
} else {// 3
READ(e.child[i]);
System.out.println(e.child[i]);
if (e.child[i].num == T - 1) {
boolean sign = false;
System.out.println(e.child[i+1].num);
if (i != 1) {// 3a
READ(e.child[i - 1]);
if (e.child[i - 1].num >= T) {
Entry y = e.child[i];
Entry z = e.child[i - 1];
for (int j = y.num; j >= 1; j--) {
y.key[j + 1] = y.key[j];
}
for (int j = y.num + 1; j >= 1; j--) {
y.child[j + 1] = y.child[j];
}
y.key[1] = e.key[i - 1];
y.child[1] = z.child[z.num + 1];
e.key[i - 1] = z.key[z.num];
y.num++;
z.num--;
e = e.child[i];
sign = true;
}
}
if (!sign && i != e.num + 1) {// 3a
READ(e.child[i + 1]);
if (e.child[i + 1].num >= T) {
Entry y = e.child[i];
Entry z = e.child[i + 1];
y.key[y.num + 1] = e.key[i];
y.child[y.num + 2] = e.child[1];
e.key[i] = z.key[1];
for (int j = 1; j <= z.num - 1; j++) {
z.key[j] = z.key[j + 1];
}
for (int j = 1; j <= z.num; j++) {
z.child[j] = z.child[j + 1];
}
y.num++;
z.num--;
e = e.child[i];
sign = true;
}
}
if (!sign) {// 3b
if (i != 1) {
READ(e.child[i - 1]);
Entry y = e.child[i - 1];
Entry z = e.child[i];
y.key[T] = e.key[i - 1];
for (int j = i - 1; j <= e.num - 1; j++) {
e.key[j] = e.key[j + 1];
}
for (int j = 1; j <= z.num; j++) {
y.key[T + j] = z.key[j];
}
for (int j = 1; j <= z.num + 1; j++) {
y.child[T + j] = z.child[j];
}
e.num--;
y.num = 2 * T - 1;
CLEAR(z);
} else {
READ(e.child[i + 1]);
Entry y = e.child[i];
Entry z = e.child[i + 1];
y.key[T] = e.key[i];
for (int j = i; j <= e.num - 1; j++) {
e.key[j] = e.key[j + 1];
}
for (int j = 1; j <= z.num; j++) {
y.key[T + j] = z.key[j];
}
for (int j = 1; j <= z.num + 1; j++) {
y.child[T + j] = z.child[j];
}
e.num--;
y.num = 2 * T - 1;
CLEAR(z);
}
}
} else {
e = e.child[i];
}
}
}
}
private EntryPosition getPrecuesor(EntryPosition ep) {
Entry e = ep.entry.child[ep.position];
while (!e.leaf) {
READ(e.child[e.num + 1]);
e = e.child[e.num + 1];
}
return new EntryPosition(e, e.num);
}
private EntryPosition getSubsequent(EntryPosition ep) {
Entry e = ep.entry.child[ep.position + 1];
while (!e.leaf) {
READ(e.child[1]);
e = e.child[1];
}
return new EntryPosition(e, 1);
}
public void printInorderTraversal() {
doPrintInorderTraversal(root);
System.out.println(" comeplete!");
}
private void doPrintInorderTraversal(Entry e) {
System.out.println(e.num);
for (int i = 1; i <= e.num; i++) {
if (!e.leaf) {
READ(e.child[i]);
doPrintInorderTraversal(e.child[i]);
}
System.out.print(e.key[i] + " ");
}
if (!e.leaf) {
READ(e.child[e.num + 1]);
doPrintInorderTraversal(e.child[e.num + 1]);
}
}
public static void main(String[] args) {
BTree bt = new BTree();
bt.insert(7);
bt.insert(13);
bt.insert(16);
bt.insert(24);
bt.insert(1);
bt.insert(3);
bt.insert(4);
bt.insert(5);
bt.insert(10);
bt.insert(11);
bt.insert(14);
bt.insert(15);
bt.insert(18);
bt.insert(19);
bt.insert(20);
bt.insert(21);
bt.insert(22);
bt.insert(25);
bt.insert(26);
bt.printInorderTraversal();
}
}