实现优先级队列(小根堆)

头条算法一面，记录一下

实现优先级队列(小根堆)

class prioQueue:
    def __init__(self, elist=[]):
        self._elems = list(elist)
        if elist:
            self.buildheap()
    def siftdown(self, e,begin, end):
        elems, i, j, = self._elems, begin , begin*2+1
        while j < end:
            if j+1<end and elems[j+1] < elems[j]:
                j = j + 1         
            if e < elems[j]:
                break
            elems[i] = elems[j]
            i, j = j , 2*j+1
        elems[i] = e
    def buildheap(self):
        end = len(self._elems)
        for i in range(end//2,-1,-1):
            self.siftdown(self._elems[i],i,end)
        return self._elems
    def peek(self):                       
        return self._elems[0]
    def dequeue(self):
        elems = self._elems
        e0 = elems[0]
        e = elems.pop()
        if len(elems) > 0:
            self.siftdown(e, 0 , len(elems))
        return e0
    def siftup(self, e, last):
        elems , i , j = self._elems, last, (last-1)//2
        while i > 0 and e < elems[j]:
            elems[i] = elems[j]
            i, j = j ,(j-1)//2
        elems[i] = e
    def enqueue(self, e):
        self._elems.append(None)
        self.siftup(e, len(self._elems)-1)
        return self._elems