当iA.heap-size2时，调用MAX-HEAPIF

Max_Heapify(A,idx,max) 
    left = 2*idx
    right = 2*idx
    if(left<max and A[left]>A[idx]) then
        largest = left
    else
        largest = idx
    if(right < max and A[right]>A[largest]) then
        largest = ritht
    
    if(largest != idx) then
        exchange A[largest] with A[idx]
        Max_Heapify(A,largest,max) 
end