Question

我已经使用Sedgewick在他的课程中讲授的算法在Python中编写了Mergesort的实现。我无法正确排序。代码有什么问题？

def merge(a, aux, lo, mid, hi):
    assert isSorted(a, lo, mid)
    assert isSorted(a, mid+1, hi)

    for k in range(lo, hi):
        aux[k] = a[k]

    i = lo
    j = mid + 1
    for k in range(lo, hi):
        if i > mid:
            a[k] = aux[j]
            j += 1
        elif j > hi:
            a[k] = aux[i]
            i += 1
        elif a[i] < a[j]:
            a[k] = aux[i]
            i += 1
        else:
            a[k] = aux[j]
            j += 1
    assert isSorted(a, lo, hi)  

def sort(a, aux, lo, hi):
    if (lo >= hi): return a
    mid = math.floor(lo + (hi-lo) / 2)

    sort(a, aux, lo, mid)
    sort(a, aux, mid+1, hi)
    merge(a, aux, lo, mid, hi)

def merge_sort(a):
    aux = [0] * len(a)
    sort(a, aux, 0, len(a))
    assert isSortedArray(a)

Answer 1

Python使用基于0的索引。你需要调整你的lo，mid，hi到0的索引。

起点是

sort(a,aux,0, len(a)-1)

无法编写Mergesort代码

1 个答案: