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#include <string>
using std::string;
#include <vector>
class CombinationIterator {
public:
string chars;
int char_length;
int combinationLength;
bool has_next = true;
std::vector<int> indices;
CombinationIterator(string characters, int combinationLength)
: chars(characters), char_length(characters.size()),
combinationLength(combinationLength) {
for (int i = 0; i < combinationLength; i++) {
indices.push_back(i);
}
}
string next() {
string result;
for (auto index : indices) {
result.push_back(chars[index]);
}
int count = 1;
while (indices[combinationLength - count] == char_length - count) {
count++;
if (count > combinationLength) {
has_next = false;
return result;
}
}
indices[combinationLength - count] += 1;
for (int i = combinationLength - count + 1; i < combinationLength; i++) {
indices[i] = indices[i - 1] + 1;
}
return result;
}
bool hasNext() {
return has_next;
}
};
/**
* Your CombinationIterator object will be instantiated and called as such:
* CombinationIterator* obj = new CombinationIterator(characters,
* combinationLength); string param_1 = obj->next(); bool param_2 =
* obj->hasNext();
*/
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