private void traverseTerminalStrings(Item i) {
if (i.shifts != null) {
for (Transition t : i.shifts) {
q.add(t);
traverseTerminalStrings(t.target);
q.pop();
}
} else {
Symbol[] str = new Symbol[q.size()];
for (int j = 0; j < q.size(); ++j) {
str[j] = q.get(j).label;
}
// add it to minimalStrings
for (Transition t : i.reduces) {
for (Transition shift : t.shifts) {
Symbol[] prev = minimalStrings.get(shift);
if (prev == null || prev.length > str.length) {
minimalStrings.put(shift, str);
}
}
}
}
}
public ShareableHashMap<Transition, Symbol[]> getMinimalStrings(NFA nfa) {
// find all begins of productions and fill initial minimal strings
Set<Item> begins = new ShareableHashSet<Item>();
for (Item i : nfa.items) {
if (i.atBegin()) {
if (i.production.containsNonTerminals()) {
begins.add(i);
} else {
traverseTerminalStrings(i);
}
}
}
for (Transition t : nfa.transitions) {
if (!(t.label instanceof NonTerminal)) {
minimalStrings.put(t, new Symbol[] {t.label});
}
}
boolean changed;
do {
changed = false;
for (Item i : begins) {
ShareableHashMap<Item, StackNode> level = new ShareableHashMap<Item, StackNode>();
level.put(i, new StackNode(null, null));
// breadth first traverse all shift transitions
// stacks join and continue with stack with minimal string length
for (int j = i.production.getLength() - 1; j >= 0 && level.size() > 0; --j) {
ShareableHashMap<Item, StackNode> nextLevel = new ShareableHashMap<Item, StackNode>();
for (Entry<Item, StackNode> e : level) {
for (Transition t : e.getKey().shifts) {
Symbol[] tstr = minimalStrings.get(t);
if (tstr != null) {
StackNode n = e.getValue();
StackNode nn = nextLevel.get(t.target);
if (nn == null) {
nextLevel.put(t.target, new StackNode(tstr, n));
} else {
if (nn.len > n.len + tstr.length) {
// replace nn
nextLevel.put(t.target, new StackNode(tstr, n));
}
}
}
}
}
level = nextLevel;
}
if (level.size() == 0) {
continue;
}
// add minimalStrings for stacks that have reached the end of i.production
for (Entry<Item, StackNode> e : level) {
StackNode n = e.getValue();
Symbol[] nstr = null;
for (Transition r : e.getKey().reduces) {
for (Transition shift : r.shifts) {
Symbol[] sstr = minimalStrings.get(shift);
if (sstr == null || sstr.length > n.len) {
if (nstr == null) {
nstr = new Symbol[n.len];
int j = n.len;
StackNode tail = n;
while (tail.prev != null) {
for (int k = tail.tstr.length - 1; k >= 0; --k) {
nstr[--j] = tail.tstr[k];
}
tail = tail.prev;
}
}
minimalStrings.put(shift, nstr);
changed = true; // TODO can we make a todo set?
}
}
}
}
}
} while (changed);
return minimalStrings;
}
