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| 1 | +# Approach: Using Doubly Linked List |
| 2 | + |
| 3 | +# Time: O(1) |
| 4 | +# Space: O(n) |
| 5 | + |
| 6 | +class Node: |
| 7 | + def __init__(self, freq): |
| 8 | + self.freq = freq |
| 9 | + self.prev = None |
| 10 | + self.next = None |
| 11 | + self.keys = set() |
| 12 | + |
| 13 | +class AllOne: |
| 14 | + |
| 15 | + def __init__(self): |
| 16 | + self.head = Node(0) # Dummy head |
| 17 | + self.tail = Node (0) # Dummy tail |
| 18 | + self.head.next = self.tail |
| 19 | + self.tail.prev = self.head |
| 20 | + self.map = {} # Mapping from key to its node |
| 21 | + |
| 22 | + |
| 23 | + def inc(self, key: str) -> None: |
| 24 | + if key in self.map: |
| 25 | + node = self.map[key] |
| 26 | + freq = node.freq |
| 27 | + node.keys.remove(key) # Remove key from current node |
| 28 | + |
| 29 | + next_node = node.next |
| 30 | + if next_node == self.tail or next_node.freq != freq + 1: |
| 31 | + # Create new node |
| 32 | + new_node = Node(freq + 1) |
| 33 | + new_node.keys.add(key) |
| 34 | + new_node.prev = node |
| 35 | + new_node.next = next_node |
| 36 | + node.next = new_node |
| 37 | + next_node.prev = new_node |
| 38 | + self.map[key] = new_node |
| 39 | + |
| 40 | + else: |
| 41 | + # Add key in the next node |
| 42 | + next_node.keys.add(key) |
| 43 | + self.map[key] = next_node |
| 44 | + |
| 45 | + # Remove the current node if it has no keys left |
| 46 | + if not node.keys: |
| 47 | + self._removeNode(node) |
| 48 | + |
| 49 | + # Key does not exist |
| 50 | + else: |
| 51 | + first_node = self.head.next |
| 52 | + if first_node == self.tail or first_node.freq > 1: |
| 53 | + # Create new node |
| 54 | + new_node = Node(1) |
| 55 | + new_node.keys.add(key) |
| 56 | + new_node.prev = self.head |
| 57 | + new_node.next = first_node |
| 58 | + self.head.next = new_node |
| 59 | + first_node.prev = new_node |
| 60 | + self.map[key] = new_node |
| 61 | + else: # Freq is 1 |
| 62 | + first_node.keys.add(key) |
| 63 | + self.map[key] = first_node |
| 64 | + |
| 65 | + |
| 66 | + def dec(self, key: str) -> None: |
| 67 | + if key not in self.map: |
| 68 | + return # Key does not exist |
| 69 | + |
| 70 | + node = self.map[key] |
| 71 | + node.keys.remove(key) |
| 72 | + freq = node.freq |
| 73 | + |
| 74 | + if freq == 1: |
| 75 | + # Remove the key from the map if freq is 1 |
| 76 | + del self.map[key] |
| 77 | + else: |
| 78 | + prev_node = node.prev |
| 79 | + if prev_node == self.head or prev_node.freq != freq - 1: |
| 80 | + # Creae a new node |
| 81 | + new_node = Node(freq - 1) |
| 82 | + new_node.keys.add(key) |
| 83 | + new_node.prev = prev_node |
| 84 | + new_node.next = node |
| 85 | + prev_node.next = new_node |
| 86 | + node.prev = new_node |
| 87 | + self.map[key] = new_node |
| 88 | + else: |
| 89 | + # Decrement the existing previous node |
| 90 | + prev_node.keys.add(key) |
| 91 | + self.map[key] = prev_node |
| 92 | + |
| 93 | + # Remove node if it has no keys left |
| 94 | + if not node.keys: |
| 95 | + self._removeNode(node) |
| 96 | + |
| 97 | + |
| 98 | + def getMaxKey(self) -> str: |
| 99 | + if self.tail.prev == self.head: |
| 100 | + return '' # No keys exist |
| 101 | + return next(iter(self.tail.prev.keys)) # Return one of the keys from tail's prev node |
| 102 | + |
| 103 | + |
| 104 | + def getMinKey(self) -> str: |
| 105 | + if self.head.next == self.tail: |
| 106 | + return '' # No keys exist |
| 107 | + return next(iter(self.head.next.keys)) # Return one of the keys from head's next node |
| 108 | + |
| 109 | + |
| 110 | + def _removeNode(self, node): |
| 111 | + prev_node = node.prev |
| 112 | + next_node = node.next |
| 113 | + |
| 114 | + prev_node.next = next_node |
| 115 | + next_node.prev = prev_node |
| 116 | + |
| 117 | + |
| 118 | + |
| 119 | + |
| 120 | +# Your AllOne object will be instantiated and called as such: |
| 121 | +# obj = AllOne() |
| 122 | +# obj.inc(key) |
| 123 | +# obj.dec(key) |
| 124 | +# param_3 = obj.getMaxKey() |
| 125 | +# param_4 = obj.getMinKey() |
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