_1286.java

packagecom.fishercoder.solutions.secondthousand;

importjava.util.ArrayList;
importjava.util.List;

publicclass_1286 {
publicstaticclassSolution1 {
publicstaticclassCombinationIterator {

List<String> list;
intindex;
intcombinationLength;
boolean[] visited;

publicCombinationIterator(Stringcharacters, intcombinationLength) {
this.index = 0;
this.list = newArrayList<>();
this.combinationLength = combinationLength;
this.visited = newboolean[characters.length()];
buildAllCombinations(characters, 0, newStringBuilder(), visited);
 }

privatevoidbuildAllCombinations(
Stringcharacters, intstart, StringBuildersb, boolean[] visited) {
if (sb.length() == combinationLength) {
list.add(sb.toString());
return;
 } else {
for (inti = start; i < characters.length(); ) {
if (!visited[i]) {
sb.append(characters.charAt(i));
visited[i] = true;
buildAllCombinations(characters, i++, sb, visited);
visited[i - 1] = false;
sb.setLength(sb.length() - 1);
 } else {
i++;
 }
 }
 }
 }

publicStringnext() {
returnlist.get(index++);
 }

publicbooleanhasNext() {
returnindex < list.size();
 }
 }
 }
}