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| 1 | +"""按特定顺序对一串数据进行排序。 |
| 2 | +排序算法的稳定性,让相等键值的记录维持次序,例如: |
| 3 | +(3,1)(3,7)(4,1)(5,6)维持次序 |
| 4 | +(3,7)(3,1)(4,1)(5,6)次序被改变""" |
| 5 | + |
| 6 | +"""Bubble Sort冒泡排序,第一次冒泡把最大的推到最上面, |
| 7 | +第二次把第二大的推到最大的后面,最多需要冒泡的次数为 |
| 8 | +元素总数减1""" |
| 9 | +def bubble_sort(list): |
| 10 | + """j为每次遍历需要比较的次数,逐次减小1""" |
| 11 | + for j in range(len(alist)-1,0,-1): |
| 12 | + for i in range(j): |
| 13 | + if alist[i] > alist[i+1]: |
| 14 | + alist[i], alist[i+1] = alist[i+1], alist[i] |
| 15 | + |
| 16 | +"""Selection sort选择排序:包括如何选出列表中的 |
| 17 | +最小值""" |
| 18 | +def selection_sort(alist): |
| 19 | + n = len(alist) |
| 20 | + """需要进行次n-1选择操作,逐次找出 |
| 21 | + 最大,次最大,,,,""" |
| 22 | + for i in range(n-1): |
| 23 | + """记录最小的位置""" |
| 24 | + min_index = i |
| 25 | + """从i+1位置开始选出最小数据""" |
| 26 | + for j in range(i+1, n): |
| 27 | + if alist[j] < alist[min_index]: |
| 28 | + min_index = j |
| 29 | + """如果选出的数据不在正确位置,进行交换""" |
| 30 | + if min_index != i: |
| 31 | + alist[i], alist[min_index] = alist[min_index], alist[i] |
| 32 | + |
| 33 | +"""Insertion Sort插入排序""" |
| 34 | +def insert_sort(alist): |
| 35 | + """从第二个位置,即下标为1的元素开始向前插入""" |
| 36 | + for i in range(1, len(alist)): |
| 37 | + for j in range(i, 0, -1): |
| 38 | + """从第i个元素向前比较,如果小于前一个元素,交换位置""" |
| 39 | + if alist[j] < alist[j-1]: |
| 40 | + alist[j], alist[j-1] = alist[j-1], alist[j] |
| 41 | + |
| 42 | +"""Quick sort快速排序""" |
| 43 | +def quick_sort(alist, start, end): |
| 44 | + if start >= end: |
| 45 | + return |
| 46 | + |
| 47 | + mid = alist[start] |
| 48 | + low = start |
| 49 | + high = end |
| 50 | + |
| 51 | + while low < high: |
| 52 | + while low < high and alist[high] >= mid: |
| 53 | + high -= 1 |
| 54 | + alist[low] = alist[high] |
| 55 | + |
| 56 | + while low < high and alist[low] < mid: |
| 57 | + low += 1 |
| 58 | + alist[high] = alist[low] |
| 59 | + alist[low] = mid |
| 60 | + quick_sort(alist, start, low-1) |
| 61 | + quick_sort(alist, low+1, end) |
| 62 | + |
| 63 | +"""Shell sort希尔排序,是改进版直接插入排序算法""" |
| 64 | +def shell_sort(alist): |
| 65 | + n = len(alist) |
| 66 | + gap = n / 2 |
| 67 | + while gap > 0: |
| 68 | + for i in range(gap, n): |
| 69 | + j = i |
| 70 | + while j>= gap and alist[j-gap] > alist[j]: |
| 71 | + alist[j-gap], alist[j] = alist[j], alist[j-gap] |
| 72 | + j -= gap |
| 73 | + gap = gap / 2 |
| 74 | + |
| 75 | +"""merge_sort归并排序""" |
| 76 | +def merge_sort(alist): |
| 77 | + if len(alist) <= 1: |
| 78 | + return alist |
| 79 | + num = len(alist)/2 |
| 80 | + left = merge_sort(alist[:num]) |
| 81 | + right = merge_sort(alist[num:]) |
| 82 | + return merge_sort(left, right) |
| 83 | + |
| 84 | +def merge(left, right): |
| 85 | + l, r = 0, 0 |
| 86 | + result = [] |
| 87 | + while l<len(left) and r<len(right): |
| 88 | + if left[l] < right[r]: |
| 89 | + result.append(left[l]) |
| 90 | + l += 1 |
| 91 | + else: |
| 92 | + result.append(right[r]) |
| 93 | + r += 1 |
| 94 | + result += left[l:] |
| 95 | + result += right[r:] |
| 96 | + return result |
| 97 | + |
| 98 | + |
| 99 | + |
| 100 | + |
| 101 | + |
| 102 | + |
| 103 | + |
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