LexGen.cpp

#include <iostream>
#include <vector>
#include <map>
#include <queue>
#include <stack>
#include <string>
#include <algorithm>

using namespace std;

class LexGen {
	public:
		int length;

		LexGen(int l) {
			length = l;
		}

		class iterator {
			int i;
			int c;
			int len;
			public:
				string str;
				iterator(string s, int l) {
					str = s;
					c = 0;
					len = l;
				}
				const string &operator*() {
					return str;
				}

				void operator++() {
					int i = len - 1;
					while(i >= 0 && str[i] == 'd') {
						str[i] = 'a';
						i--;
					}
					if(i >= 0) {
						str[i]++;
					}
					c++;
				}

				bool operator!=(const iterator &r) {
					return str.compare(r.str) != 0;
				}
		};

		iterator begin() {
			iterator it("aaa", length);
			return it;
		}

		iterator end() {
			return iterator("ddd", length);
		}

};

int main() {
	LexGen lg(3);
	for(auto it = lg.begin(); it != lg.end(); ++it) {
		cout << *it << endl;
	}

	return 0;
}