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  1. #include <iostream>
  2. #include <sstream>
  3. #include <list>
  4. #include <cassert>
  5.  
  6. template <typename T>
  7. class sequence
  8. {
  9. private:
  10. 	std::list<T> _l;
  11. 	typename std::list<T>::iterator _i;
  12. public:
  13. 	using value_type = T;
  14. 	using size_type = typename std::list<T>::size_type;
  15.  
  16. 	size_type size() const {
  17. 		return _l.size();
  18. 	}
  19.  
  20. 	T current() const {
  21. 		assert(is_current_valid());
  22. 		return *_i;
  23. 	}
  24.  
  25. 	size_type current_index() const {
  26. 		return _i - _l.begin();
  27. 	}
  28.  
  29. 	void increase_current() {
  30. 		if (is_current_valid()) {
  31. 			++_i;
  32. 		}
  33. 	}
  34.  
  35. 	void decrease_current() {
  36. 		if (_i != _l.begin()) {
  37. 			--_i;
  38. 		}
  39. 	}
  40.  
  41. 	void reset_current() {
  42. 		_i = _l.begin();
  43. 	}
  44.  
  45. 	bool is_current_valid() const {
  46. 		// "is_item"
  47. 		return _i != _l.end();
  48. 	}
  49.  
  50. 	void remove_current() {
  51. 		assert(is_current_valid());
  52. 		// _i takes the next current element, eventually end()
  53. 		_i = _l.erase(_i);
  54. 	}
  55.  
  56. 	void insert_before(const value_type &entry) {
  57. 		// _i is always the newly inserted element
  58. 		_i = _l.insert(_i, entry);
  59. 	}
  60.  
  61. 	void insert_after(const value_type &entry) {
  62. 		// _i is always the newly inserted element
  63. 		assert(is_current_valid());
  64. 		_i = _l.insert(++_i, entry);
  65. 	}
  66.  
  67. 	friend std::ostream &operator<<(std::ostream &os, sequence const &s) {
  68. 		for (auto it = s._l.begin(); it != s._l.end(); ++it) {
  69. 			if (it != s._l.begin()) {
  70. 				os << " " << *it;
  71. 			} else {
  72. 				os << *it;
  73. 			}
  74. 		}
  75. 		return os;
  76. 	}
  77.  
  78. 	sequence() : _l(), _i(_l.end()) {}
  79. };
  80.  
  81. int main() {
  82. 	sequence<std::size_t> numbers;
  83. 	numbers.insert_before(21); // insert 21, then points to 21
  84. 	numbers.insert_after(33);  // 33 after 21, then points to 33
  85. 	numbers.insert_before(22); // 22 before 21, then points to 22
  86. 	std::cout << numbers << std::endl;
  87.  
  88. 	// Programmatically check if the result is the requested one
  89. 	const std::string expected = "21 22 33";
  90. 	std::stringstream output;
  91. 	output << numbers;
  92. 	if (output.str() != expected) {
  93. 		std::cerr << "Error!" << std::endl;
  94. 		return 1;
  95. 	}
  96.  
  97. 	return 0;
  98. }
  99.  
Success #stdin #stdout 0s 3464KB
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stdin
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Standard input is empty
stdout
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21 22 33
https://ideone.com/BDtKdg
language:
C++14 (gcc 8.3)
created:
9 years ago
visibility:
public

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