快速排序
发现自己写起来很不顺手,得从最右边找出pivot元素是最方便的!
以最左边的元素作为pivot的代码,看到好多坑:
def qsort(arr, left, right): if left >= right: return pivot = arr[left] p = left+1 for i in range(left+1, right+1): if arr[i] < pivot: arr[i], arr[p] = arr[p], arr[i] p += 1 partition_index = p-1 arr[left], arr[partition_index] = arr[partition_index], arr[left] qsort(arr, left, partition_index-1) qsort(arr, partition_index+1, right) def qsort2(arr, left, right): if left >= right: return pivot = arr[right] index = left for i in range(left, right): if arr[i] < pivot: arr[i], arr[index] = arr[index], arr[i] index += 1 arr[index], arr[right] = arr[right], arr[index] qsort2(arr, left, index-1) qsort2(arr, index+1, right) from random import randint a=[] for i in range(30): a.append(randint(0, 20)) print a qsort2(a, 0, len(a)-1) print a
输出:
[12, 4, 19, 2, 15, 13, 16, 2, 4, 1, 0, 13, 10, 1, 11, 15, 13, 7, 8, 6, 12, 20, 18, 20, 20, 3, 7, 5, 11, 11]
[0, 1, 1, 2, 2, 3, 4, 4, 5, 6, 7, 7, 8, 10, 11, 11, 11, 12, 12, 13, 13, 13, 15, 15, 16, 18, 19, 20, 20, 20]
partition有三种思路写法:
def patition(arr, l, r): pivot = arr[l] i, j = l+1, r while i <= j: if arr[i] <= pivot: i += 1 else: arr[i], arr[j] = arr[j], arr[i] j -= 1 arr[l], arr[j] = arr[j], arr[l] return j def patition2(arr, l, r): pivot = arr[l] index = l+1 for i in range(l+1, r+1): if arr[i] < pivot: arr[i], arr[index] = arr[index], arr[i] index += 1 arr[l], arr[index-1] = arr[index-1], arr[l] return index-1 # TODO