▶ 书中第六章部分程序，包括在加上自己补充的代码，B-树
● B-树
package package01; import edu.princeton.cs.algs4.StdOut; public class class01<Key extends Comparable<Key>, Value>
{
private static final int M = 4; // 子节点数量为 M-1 private Node root; // 根节点
private int height; // 树高
private int n; // 键值对的数量 private static final class Node // 节点类
{
private int m; // 当前子节点数量
private Entry[] children = new Entry[M]; // 子节点列表 private Node(int k) // 构造有 k 个子节点的节点
{
m = k;
}
} private static class Entry // 子节点列表类，内部结点使用 key 和 next，外部节点使用 key 和 value
{
private Comparable key;
private Node next;
private final Object val; public Entry(Comparable inputKey, Object inputVal, Node inputNext)
{
key = inputKey;
next = inputNext;
val = inputVal;
}
} public class01()
{
root = new Node(0);
} public int size()
{
return n;
} public boolean isEmpty()
{
return size() == 0;
} public int height()
{
return height;
} public Value get(Key key)
{
if (key == null)
throw new IllegalArgumentException("\n<get> key == null.\n");
return search(root, key, height);
} private Value search(Node x, Key key, int ht) // 穿如数奉告，每次进入更深层时减一
{
Entry[] children = x.children;
if (ht == 0) // 到达的是叶节点，遍历列表
{
for (int j = 0; j < x.m; j++)
{
if (eq(key, children[j].key)) // 找到了，返回 val
return (Value)children[j].val;
}
}
else // 到达的是内部节点
{
for (int j = 0; j < x.m; j++)
{
if (j == x.m - 1 || less(key, children[j + 1].key)) // j 到达最后或找到合适的子节点，进入下一层
return search(children[j].next, key, ht - 1);
}
}
return null;
} public void put(Key key, Value val)
{
if (key == null)
throw new IllegalArgumentException("\n<put> key == null.\n");
Node u = insert(root, key, val, height); // 执行插入插座并调整总键值对数量
n++;
if (u == null) // 没有需要调整的节点
return;
Node t = new Node(2); // 根节点需要分裂，新建一个具有 2 个子节点的节点
t.children[0] = new Entry(root.children[0].key, null, root); // 第一个子节点是原来的根节点
t.children[1] = new Entry(u.children[0].key, null, u); // 第二个子节点是插入操作导致新增加的节点
root = t; // root 编程新建的 t，并增加一层树高
height++;
} private Node insert(Node h, Key key, Value val, int ht)
{
int j;
Entry t = new Entry(key, val, null);
if (ht == 0) // 到达的是外部节点
{
for (j = 0; j < h.m; j++)
{
if (less(key, h.children[j].key)) // 找到合适的位置就脱出循环
break;
}
}
else // 到达的是内部节点
{
for (j = 0; j < h.m; j++)
{
if ((j + 1 == h.m) || less(key, h.children[j + 1].key)) // j 到达最后或找到合适的子节点，进入下一层
{
Node u = insert(h.children[j++].next, key, val, ht - 1);// 在 h.children[j] 进行插入
if (u == null)
return null;
t.key = u.children[0].key; // 把 u 的信息改造到 t 上
t.next = u; // 真正 next 是在这里赋值的，指向下一个子节点
break;
}
}
}
for (int i = h.m; i > j; i--) // 调整本层，排在插入位置之后的元素都向后移动一格
h.children[i] = h.children[i - 1];
h.children[j] = t; // 插入节点 t，增加 h 的子节点数量
h.m++;
return (h.m < M) ? null : split(h); // 节点 h 满了就需要扩容，返回扩容后多出来的节点，用于上一层调整
} private Node split(Node h) // 分裂节点 h，并返回分裂出来的后一半节点
{
Node t = new Node(M / 2);
h.m = M / 2; // 改 h 的子节点数为一半，相当于废弃后一半记录
for (int j = 0; j < M / 2; j++) // 后一半元素搬进 t
t.children[j] = h.children[M / 2 + j];
return t;
} public String toString()
{
return toStringKernel(root, height, "") + "\n";
} private String toStringKernel(Node h, int ht, String indent) // 遍历树转化为字符串
{
StringBuilder s = new StringBuilder();
Entry[] children = h.children;
if (ht == 0) // 叶节点，输出
{
for (int j = 0; j < h.m; j++)
s.append(indent + children[j].key + " " + children[j].val + "\n"); // 注意换行
}
else // 非叶节点，遍历子节点列表
{
for (int j = 0; j < h.m; j++)
{
if (j > 0)
s.append(indent + "(" + children[j].key + ")\n");
s.append(toStringKernel(children[j].next, ht - 1, indent + " "));
}
}
return s.toString();
} private boolean less(Comparable k1, Comparable k2)
{
return k1.compareTo(k2) < 0;
} private boolean eq(Comparable k1, Comparable k2)
{
return k1.compareTo(k2) == 0;
} public static void main(String[] args) // 输入一堆网站和 IP 建立 B-树
{
class01<String, String> st = new class01<String, String>(); st.put("www.cs.princeton.edu", "128.112.136.12");
st.put("www.cs.princeton.edu", "128.112.136.11");
st.put("www.princeton.edu", "128.112.128.15");
st.put("www.yale.edu", "130.132.143.21");
st.put("www.simpsons.com", "209.052.165.60");
st.put("www.apple.com", "17.112.152.32");
st.put("www.amazon.com", "207.171.182.16");
st.put("www.ebay.com", "66.135.192.87");
st.put("www.cnn.com", "64.236.16.20");
st.put("www.google.com", "216.239.41.99");
st.put("www.nytimes.com", "199.239.136.200");
st.put("www.microsoft.com", "207.126.99.140");
st.put("www.dell.com", "143.166.224.230");
st.put("www.slashdot.org", "66.35.250.151");
st.put("www.espn.com", "199.181.135.201");
st.put("www.weather.com", "63.111.66.11");
st.put("www.yahoo.com", "216.109.118.65"); StdOut.println("cs.princeton.edu: " + st.get("www.cs.princeton.edu"));
StdOut.println("hardvardsucks.com: " + st.get("www.harvardsucks.com"));
StdOut.println("simpsons.com: " + st.get("www.simpsons.com"));
StdOut.println("apple.com: " + st.get("www.apple.com"));
StdOut.println("ebay.com: " + st.get("www.ebay.com"));
StdOut.println("dell.com: " + st.get("www.dell.com"));
StdOut.println(); StdOut.println("size: " + st.size());
StdOut.println("height: " + st.height());
StdOut.println(st);
StdOut.println();
}
}
● 测试函输出，即生成的树
cs.princeton.edu: 128.112.136.12
hardvardsucks.com: null
simpsons.com: 209.052.165.60
apple.com: 17.112.152.32
ebay.com: 66.135.192.87
dell.com: 143.166.224.230 size: 17
height: 2
www.amazon.com 207.171.182.16
www.apple.com 17.112.152.32
www.cnn.com 64.236.16.20
(www.cs.princeton.edu)
www.cs.princeton.edu 128.112.136.12
www.cs.princeton.edu 128.112.136.11
www.dell.com 143.166.224.230
(www.ebay.com)
www.ebay.com 66.135.192.87
www.espn.com 199.181.135.201
www.google.com 216.239.41.99
(www.microsoft.com)
www.microsoft.com 207.126.99.140
www.nytimes.com 199.239.136.200
(www.princeton.edu)
www.princeton.edu 128.112.128.15
www.simpsons.com 209.052.165.60
(www.slashdot.org)
www.slashdot.org 66.35.250.151
www.weather.com 63.111.66.11
(www.yahoo.com)
www.yahoo.com 216.109.118.65
www.yale.edu 130.132.143.21