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* Retranslate the complete English edition from Simplified Chinese * Polish three English explanations after reader-focused review
138 lines
4.0 KiB
Python
138 lines
4.0 KiB
Python
"""
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File: my_heap.py
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Created Time: 2023-02-23
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Author: krahets (krahets@163.com)
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"""
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import sys
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from pathlib import Path
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sys.path.append(str(Path(__file__).parent.parent))
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from modules import print_heap
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class MaxHeap:
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"""Max heap"""
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def __init__(self, nums: list[int]):
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"""Constructor: build a heap from the input list"""
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# Place the list elements in the heap without changing their order
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self.max_heap = nums
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# Sift down from every non-leaf node
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for i in range(self.parent(self.size() - 1), -1, -1):
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self.sift_down(i)
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def left(self, i: int) -> int:
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"""Get the left child index"""
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return 2 * i + 1
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def right(self, i: int) -> int:
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"""Get the right child index"""
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return 2 * i + 2
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def parent(self, i: int) -> int:
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"""Get the parent index"""
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return (i - 1) // 2 # Floor division
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def swap(self, i: int, j: int):
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"""Swap elements"""
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self.max_heap[i], self.max_heap[j] = self.max_heap[j], self.max_heap[i]
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def size(self) -> int:
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"""Get the heap size"""
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return len(self.max_heap)
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def is_empty(self) -> bool:
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"""Check whether the heap is empty"""
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return self.size() == 0
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def peek(self) -> int:
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"""Access the top element of the heap"""
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return self.max_heap[0]
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def push(self, val: int):
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"""Push an element onto the heap"""
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# Add a node
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self.max_heap.append(val)
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# Sift up
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self.sift_up(self.size() - 1)
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def sift_up(self, i: int):
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"""Sift up starting from node i"""
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while True:
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# Get the parent of node i
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p = self.parent(i)
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# Stop sifting when the root has been passed or the node needs no repair
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if p < 0 or self.max_heap[i] <= self.max_heap[p]:
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break
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# Swap the two nodes
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self.swap(i, p)
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# Continue sifting up
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i = p
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def pop(self) -> int:
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"""Pop an element from the heap"""
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# Handle an empty heap
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if self.is_empty():
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raise IndexError("Heap is empty")
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# Swap the root with the rightmost leaf on the last level (swap the first and last elements)
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self.swap(0, self.size() - 1)
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# Remove a node
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val = self.max_heap.pop()
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# Sift down
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self.sift_down(0)
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# Return the top element of the heap
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return val
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def sift_down(self, i: int):
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"""Sift down starting from node i"""
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while True:
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# Find the node with the largest value among i, l, and r, and store its index in ma
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l, r, ma = self.left(i), self.right(i), i
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if l < self.size() and self.max_heap[l] > self.max_heap[ma]:
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ma = l
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if r < self.size() and self.max_heap[r] > self.max_heap[ma]:
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ma = r
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# Stop if node i is largest or both child indices l and r are out of bounds
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if ma == i:
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break
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# Swap the two nodes
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self.swap(i, ma)
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# Continue sifting down
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i = ma
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def print(self):
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"""Print the heap (binary tree)"""
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print_heap(self.max_heap)
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"""Driver code"""
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if __name__ == "__main__":
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# Initialize a max heap
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max_heap = MaxHeap([9, 8, 6, 6, 7, 5, 2, 1, 4, 3, 6, 2])
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print("\nAfter building a heap from the input list:")
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max_heap.print()
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# Get the top element of the heap
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peek = max_heap.peek()
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print(f"\nTop element of the heap: {peek}")
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# Push an element onto the heap
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val = 7
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max_heap.push(val)
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print(f"\nAfter pushing element {val} onto the heap:")
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max_heap.print()
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# Pop the top element from the heap
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peek = max_heap.pop()
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print(f"\nAfter popping top element {peek} from the heap:")
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max_heap.print()
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# Get the heap size
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size = max_heap.size()
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print(f"\nNumber of elements in the heap: {size}")
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# Check whether the heap is empty
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is_empty = max_heap.is_empty()
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print(f"\nIs the heap empty: {is_empty}")
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