package learn.btree;/************************************************************************* *  Compilation:  javac BTree.java *  Execution:    java BTree * *  B-tree. * *  Limitations *  ----------- *   -  Assumes M is even and M >= 4 *   -  should b be an array of children or list (it would help with *      casting to make it a list) * *   http://algs4.cs.princeton.edu/62btrees/BTree.java.html *************************************************************************/public class BTree
    
     , Value>  {    private static final int NODE_MAX_CHILD = 4;    // max children per B-tree node = M-1    private Node root;             // root of the B-tree    private int treeHeight;                // height of the B-tree    private int kvNum;                 // number of key-value pairs in the B-tree    // helper B-tree node data type    private static final class Node {        private int childNum;                             // number of children        private Entry[] children = new Entry[NODE_MAX_CHILD];   // the array of children        private Node(int k) { childNum = k; }             // create a node with k children    }    // internal nodes: only use key and next    // external nodes: only use key and value    private static class Entry {        private Comparable key;        private Object value;        private Node next;     // helper field to iterate over array entries        public Entry(Comparable key, Object value, Node next) {            this.key   = key;            this.value = value;            this.next  = next;        }    }    // constructor    public BTree() { root = new Node(0); }    // return number of key-value pairs in the B-tree    public int size() { return kvNum; }    // return height of B-tree    public int height() { return treeHeight; }    // search for given key, return associated value; return null if no such key    public Value get(Key key) { return search(root, key, treeHeight); }    private Value search(Node x, Key key, int ht) {        Entry[] children = x.children;        // external node        if (ht == 0) {            for (int j = 0; j < x.childNum; j++) {                if (eq(key, children[j].key)) return (Value) children[j].value;            }        }        // internal node        else {            for (int j = 0; j < x.childNum; j++) {                if (j+1 == x.childNum || less(key, children[j+1].key))                    return search(children[j].next, key, ht-1);            }        }        return null;    }    // insert key-value pair    // add code to check for duplicate keys    public void put(Key key, Value value) {        Node u = insert(root, key, value, treeHeight);        kvNum++;        if (u == null) return;        // need to split root        Node t = new Node(2);        t.children[0] = new Entry(root.children[0].key, null, root);        t.children[1] = new Entry(u.children[0].key, null, u);        root = t;        treeHeight++;    }    private Node insert(Node h, Key key, Value value, int ht) {        int j;        Entry t = new Entry(key, value, null);        // external node        if (ht == 0) {            for (j = 0; j < h.childNum; j++) {                if (less(key, h.children[j].key)) break;            }        }        // internal node        else {            for (j = 0; j < h.childNum; j++) {                if ((j+1 == h.childNum) || less(key, h.children[j+1].key)) {                    Node u = insert(h.children[j++].next, key, value, ht-1);                    if (u == null) return null;                    t.key = u.children[0].key;                    t.next = u;                    break;                }            }        }        for (int i = h.childNum; i > j; i--) h.children[i] = h.children[i-1];        h.children[j] = t;        h.childNum++;        if (h.childNum < NODE_MAX_CHILD) return null;        else         return split(h);    }    // split node in half    private Node split(Node h) {        Node t = new Node(NODE_MAX_CHILD/2);        h.childNum = NODE_MAX_CHILD/2;        for (int j = 0; j < NODE_MAX_CHILD/2; j++)            t.children[j] = h.children[NODE_MAX_CHILD/2+j];        return t;    }    // for debugging    public String toString() {        return toString(root, treeHeight, "") + "\n";    }    private String toString(Node h, int ht, String indent) {        String s = "";        Entry[] children = h.children;        if (ht == 0) {            for (int j = 0; j < h.childNum; j++) {                s += indent + children[j].key + " " + children[j].value + "\n";            }        }        else {            for (int j = 0; j < h.childNum; j++) {                if (j > 0) s += indent + "(" + children[j].key + ")\n";                s += toString(children[j].next, ht-1, indent + "     ");            }        }        return s;    }    // comparison functions - make Comparable instead of Key to avoid casts    private boolean less(Comparable k1, Comparable k2) {        return k1.compareTo(k2) < 0;    }    private boolean eq(Comparable k1, Comparable k2) {        return k1.compareTo(k2) == 0;    }    /*************************************************************************     *  test client     *************************************************************************/    public static void main(String[] args) {        BTree
     
       st = new BTree
      
       ();//      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");        System.out.println("cs.princeton.edu:  " + st.get("www.cs.princeton.edu"));        System.out.println("hardvardsucks.com: " + st.get("www.harvardsucks.com"));        System.out.println("simpsons.com:      " + st.get("www.simpsons.com"));        System.out.println("apple.com:         " + st.get("www.apple.com"));        System.out.println("ebay.com:          " + st.get("www.ebay.com"));        System.out.println("dell.com:          " + st.get("www.dell.com"));        System.out.println();        System.out.println("size:    " + st.size());        System.out.println("height:  " + st.height());        System.out.println(st);        System.out.println();    }}