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phishman3579phishman3579
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Code simplification in Ternary Search Tree
1 parent 96ad312 commit 833341a

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2 files changed

+66
-50
lines changed

2 files changed

+66
-50
lines changed

‎src/com/jwetherell/algorithms/data_structures/TernarySearchTree.java‎

Lines changed: 64 additions & 50 deletions
Original file line numberDiff line numberDiff line change
@@ -47,13 +47,14 @@ public boolean add(C value) {
4747
return false;
4848

4949
final int before = size;
50-
if (root == null) {
51-
this.root = insert(null, null, value, 0);;
52-
} else {
50+
if (root == null)
51+
this.root = insert(null, null, value, 0);
52+
else
5353
insert(null, root, value, 0);
54-
}
5554
final int after = size;
56-
return (before<after);
55+
56+
// Successful if the size has increased by one
57+
return (before==(after-1));
5758
}
5859

5960
private Node insert(Node parent, Node node, C value, int idx) {
@@ -99,38 +100,44 @@ public C remove(C value) {
99100
// Find the node
100101
final Node node = search(root, value, 0);
101102

102-
// If node was found, remove from tree
103-
if (node != null) {
104-
if (node.isWord) {
105-
node.isWord = false;
106-
remove(node);
107-
size--;
108-
return value;
109-
}
110-
}
111-
return null;
103+
// If node was not found or the node is not a "word"
104+
if (node == null || !node.isWord)
105+
return null;
106+
107+
// Node was found, remove from tree if possible
108+
node.isWord = false;
109+
remove(node);
110+
size--;
111+
return value;
112112
}
113113

114114
private void remove(Node node) {
115+
// If node is a "word", stop the recursive pruning
116+
if (node.isWord)
117+
return;
118+
119+
// If node has at least one child, we cannot prune it.
120+
if (node.loKid!=null || node.kid!=null || node.hiKid!=null)
121+
return;
122+
123+
// Node has no children, prune the node
115124
final Node parent = node.parent;
125+
if (parent != null) {
126+
// Remove node from parent
127+
if (parent.loKid==node) {
128+
parent.loKid = null;
129+
} else if (parent.hiKid==node) {
130+
parent.hiKid = null;
131+
} else if (parent.kid==node) {
132+
parent.kid = null;
133+
}
116134

117-
// If node does not represent a word and has no children
118-
if (!node.isWord && node.loKid==null && node.kid==null && node.hiKid==null) {
119-
if (parent != null) {
120-
// Remove node from parent
121-
if (parent.loKid==node) {
122-
parent.loKid = null;
123-
} else if (parent.hiKid==node) {
124-
parent.hiKid = null;
125-
} else if (parent.kid==node) {
126-
parent.kid = null;
127-
}
128-
// Go up the tree and prune
135+
// If parent is not a "word" node, go up the tree and prune if possible
136+
if (!node.isWord)
129137
remove(parent);
130-
} else {
131-
// If node doesn't have a parent, it's root.
132-
this.root = null;
133-
}
138+
} else {
139+
// If node doesn't have a parent, it's root.
140+
this.root = null;
134141
}
135142
}
136143

@@ -168,8 +175,10 @@ private Node search(Node node, C value, int idx) {
168175
return search(node.loKid, value, idx);
169176
if (c > node.character)
170177
return search(node.hiKid, value, idx);
171-
if (++idx < value.length())
172-
return search(node.kid, value, idx);
178+
if (idx < (value.length()-1)) {
179+
// c == node.char and there is still some characters left in the search string
180+
return search(node.kid, value, ++idx);
181+
}
173182
return node;
174183
}
175184

@@ -182,24 +191,33 @@ public int size() {
182191
public boolean validate() {
183192
if (this.root == null)
184193
return true;
185-
186194
return validate(root);
187195
}
188196

189197
private boolean validate(Node node) {
198+
boolean result = false;
190199
if (node.loKid != null) {
191200
if (node.loKid.character >= node.character)
192201
return false;
193-
return validate(node.loKid);
202+
result = validate(node.loKid);
203+
if (!result)
204+
return false;
194205
}
206+
195207
if (node.kid != null) {
196-
return validate(node.kid);
208+
result = validate(node.kid);
209+
if (!result)
210+
return false;
197211
}
212+
198213
if (node.hiKid != null) {
199214
if (node.hiKid.character <= node.character)
200215
return false;
201-
return validate(node.hiKid);
216+
result = validate(node.hiKid);
217+
if (!result)
218+
return false;
202219
}
220+
203221
return true;
204222
}
205223

@@ -249,23 +267,20 @@ public static <C extends CharSequence> String getString(TernarySearchTree<C> tre
249267

250268
protected static String getString(Node node, String prefix, String previousString, boolean isTail) {
251269
final StringBuilder builder = new StringBuilder();
252-
final String string;
253-
final String temp = String.valueOf(node.character);
270+
String string = "";
254271
if (previousString != null)
255-
string = previousString + temp;
256-
else
257-
string = temp;
272+
string = previousString;
258273
builder.append(prefix + (isTail ? "└── " : "├── ") + ((node.isWord == true) ?
259-
("(" + node.character + ") " + string)
274+
("(" + node.character + ") " + string+String.valueOf(node.character))
260275
:
261276
node.character) + "\n"
262277
);
263278
if (node.loKid != null)
264-
builder.append(getString(node.loKid, prefix + (isTail ? " " : "│ "), string.substring(0, string.length()-1), false));
279+
builder.append(getString(node.loKid, prefix + (isTail ? " " : "│ "), string, false));
265280
if (node.kid != null)
266-
builder.append(getString(node.kid, prefix + (isTail ? " " : "│ "), string, false));
281+
builder.append(getString(node.kid, prefix + (isTail ? " " : "│ "), string+String.valueOf(node.character), false));
267282
if (node.hiKid != null)
268-
builder.append(getString(node.hiKid, prefix + (isTail ? " " : "│ "), string.substring(0, string.length()-1), true));
283+
builder.append(getString(node.hiKid, prefix + (isTail ? " " : "│ "), string, true));
269284
return builder.toString();
270285
}
271286
}
@@ -372,20 +387,19 @@ protected TreeIterator(TernarySearchTree<C> tree) {
372387

373388
private void getNodesWhichRepresentsWords(TernarySearchTree.Node node, String string, java.util.Map<TernarySearchTree.Node,String> nodesMap) {
374389
final StringBuilder builder = new StringBuilder(string);
375-
builder.append(node.character);
376390
if (node.isWord)
377391
nodesMap.put(node,builder.toString());
378392
if (node.loKid != null) {
379393
Node child = node.loKid;
380-
getNodesWhichRepresentsWords(child, builder.subSequence(0, builder.length()-1).toString(), nodesMap);
394+
getNodesWhichRepresentsWords(child, builder.toString(), nodesMap);
381395
}
382396
if (node.kid != null) {
383397
Node child = node.kid;
384-
getNodesWhichRepresentsWords(child, builder.toString(), nodesMap);
398+
getNodesWhichRepresentsWords(child, builder.append(node.character).toString(), nodesMap);
385399
}
386400
if (node.hiKid != null) {
387401
Node child = node.hiKid;
388-
getNodesWhichRepresentsWords(child, builder.subSequence(0, builder.length()-1).toString(), nodesMap);
402+
getNodesWhichRepresentsWords(child, builder.toString(), nodesMap);
389403
}
390404
}
391405

‎test/com/jwetherell/algorithms/data_structures/test/TernarySearchTreeTests.java‎

Lines changed: 2 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -30,6 +30,8 @@ public void test1() {
3030
tests.add("CAT");
3131
tests.add("BE");
3232
tests.add("B");
33+
tests.add("DAD");
34+
tests.add("APPLE");
3335

3436
final TernarySearchTree<String> bst = new TernarySearchTree<String>();
3537

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