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| 1 | +class ListNode: |
| 2 | + def __init__(self, val, next): |
| 3 | + self.val = val |
| 4 | + self.next = next |
| 5 | + |
| 6 | + |
| 7 | +class LinkedList: |
| 8 | + def __init__(self): |
| 9 | + # creating service node: |
| 10 | + self.head = ListNode(None, None) |
| 11 | + self.tail = self.head |
| 12 | + self.len = 0 |
| 13 | + |
| 14 | + def insert(self, previous_node, val): |
| 15 | + if not isinstance(previous_node, ListNode): |
| 16 | + raise TypeError("Expected previous_node to be" |
| 17 | + "ListNode instance") |
| 18 | + new_node = ListNode(val, previous_node.next) |
| 19 | + previous_node.next = new_node |
| 20 | + self.len += 1 |
| 21 | + if new_node.next is None: |
| 22 | + self.tail = new_node |
| 23 | + return new_node |
| 24 | + |
| 25 | + def push_front(self, val): |
| 26 | + return self.insert(self.head, val) |
| 27 | + |
| 28 | + def push_back(self, val): |
| 29 | + return self.insert(self.tail, val) |
| 30 | + |
| 31 | + def remove(self, node): |
| 32 | + if not isinstance(node, ListNode): |
| 33 | + raise TypeError("Expected node to be" |
| 34 | + "ListNode instance") |
| 35 | + if self.len < 1: |
| 36 | + raise ValueError('Trying to remove item from empty list') |
| 37 | + prev_node = self.head |
| 38 | + while prev_node is not None and prev_node.next != node: |
| 39 | + prev_node = prev_node.next |
| 40 | + if prev_node is not None: |
| 41 | + prev_node.next = node.next |
| 42 | + self.len -= 1 |
| 43 | + if prev_node.next is None: |
| 44 | + self.tail = prev_node |
| 45 | + return node.val |
| 46 | + else: |
| 47 | + raise ValueError('Node provided to remove()' |
| 48 | + 'was not found in the list') |
| 49 | + |
| 50 | + def pop_back(self): |
| 51 | + return self.remove(self.tail) |
| 52 | + |
| 53 | + def pop_front(self): |
| 54 | + # self.head.next may be Null. It is checked in self.remove() |
| 55 | + return self.remove(self.head.next) |
| 56 | + |
| 57 | + def __len__(self): |
| 58 | + # This function is for using len(x). |
| 59 | + return self.len |
| 60 | + |
| 61 | + # Following functions are just for easier debugging and testing: |
| 62 | + |
| 63 | + def get_node_by_index(self, i): |
| 64 | + # Service node is supposed to be node 0 |
| 65 | + if i < 0: |
| 66 | + i += self.len + 1 |
| 67 | + if not (0 <= i <= self.len): |
| 68 | + raise IndexError('List index out of range') |
| 69 | + res = self.head |
| 70 | + for i in range(i): |
| 71 | + res = res.next |
| 72 | + return res |
| 73 | + |
| 74 | + def insert_by_index(self, i, val): |
| 75 | + prev_node = self.get_node_by_index(i) |
| 76 | + return self.insert(prev_node, val) |
| 77 | + |
| 78 | + def remove_by_index(self, i): |
| 79 | + node = self.get_node_by_index(i) |
| 80 | + self.remove(node.next) |
| 81 | + |
| 82 | + def __getitem__(self, i): |
| 83 | + # This function is for using x[i]. |
| 84 | + # We add 1 because self.get_node_by_index(0) returns service node |
| 85 | + return self.get_node_by_index(i + 1).val |
| 86 | + |
| 87 | + def __repr__(self): |
| 88 | + # This function is for visualization. |
| 89 | + # It allows to use print() for List |
| 90 | + max_show = 10 |
| 91 | + show_len = min(len(self), max_show) |
| 92 | + elements_repr = list(map(str, [self[i] for i in range(show_len)])) |
| 93 | + if len(self) > max_show: |
| 94 | + elements_repr.append('...') |
| 95 | + return f'List({len(self)} elements): [{", ".join(elements_repr)}]' |
| 96 | + |
| 97 | + |
| 98 | +if __name__ == '__main__': |
| 99 | + x = LinkedList() |
| 100 | + x.push_front(1) |
| 101 | + print(x) |
| 102 | + x.push_front(10) |
| 103 | + print(x) |
| 104 | + x.push_front(100) |
| 105 | + print(x) |
| 106 | + x.push_front(1000) |
| 107 | + print(x) |
| 108 | + x.insert_by_index(2, 5) |
| 109 | + print(x) |
| 110 | + x.insert_by_index(1, 7) |
| 111 | + print(x) |
| 112 | + x.insert_by_index(-1, 70) |
| 113 | + print(x) |
| 114 | + x.insert_by_index(-1, 80) |
| 115 | + print(x) |
| 116 | + x.insert_by_index(-2, 'Text') |
| 117 | + print(x) |
| 118 | + x.remove_by_index(2) |
| 119 | + print(x) |
| 120 | + x.pop_front() |
| 121 | + print(x) |
| 122 | + x.pop_back() |
| 123 | + print(x) |
| 124 | + x.push_back('Back') |
| 125 | + print(x) |
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