python计算最小优先级队列代码分享

代码如下:

# -*- coding: utf-8 -*-

class heap(object):

@classmethod def parent(cls, i): “””父结点下标””” return int((i – 1) >> 1);

@classmethod def left(cls, i): “””左儿子下标””” return (i 0, “heap underflow” val = self[0] tail = heap_size – 1 self[0] = self[tail] self.min_heapify(self, 0, tail) self.pop(tail) return val

def decrease_key(self, i, key): “””将i处的值减少到key,伪码如下: heap-decrease-key(a, i, key) 1 if key > a[i] 2 then error “new key is larger than current key” 3 a[i] ← key 4 while i > 1 and a[parent(i)] > a[i] // 不是根结点且父结点更大时 5 do exchange a[i] ↔ a[parent(i)] // 交换两元素 6 i ← parent(i) // 指向父结点位置

t(n) = θ(lgn) “”” val = self[i] assert key 0 and self[parent(i)] > self[i]: self[i], self[parent(i)] = self[parent(i)], self[i] i = parent(i)

def insert(self, key): “””将key插入a,伪码如下: min-heap-insert(a, key) 1 heap-size[a] ← heap-size[a] + 1 // 对元素个数增加 2 a[heap-size[a]] ← +∞ // 初始新增加元素为+∞ 3 heap-decrease-key(a, heap-size[a], key) // 将新增元素减少到key

t(n) = θ(lgn) “”” self.append(float(‘inf’)) self.decrease_key(len(self) – 1, key)

if __name__ == ‘__main__’: import random

keys = range(10) random.shuffle(keys) print(keys)

queue = minpriorityqueue() # 插入方式建最小堆 for i in keys: queue.insert(i) print(queue)

print(‘*’ * 30)

for i in range(len(queue)): val = i % 3 if val == 0: val = queue.extract_min() # 去除并返回最小元素 elif val == 1: val = queue.minimum() # 返回最小元素 else: val = queue[1] – 10 queue.decrease_key(1, val) # queue[1]减少10 print(queue, val)

print([queue.extract_min() for i in range(len(queue))])