【Python】Codility in Python : Lesson 9 - Maximum slice problem【MaxDoubleSliceSum】

Maximum slice problem 第一題：【MaxDoubleSliceSum】
Find the maximal sum of any double slice.

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A non-empty zero-indexed array A consisting of N integers is given.

A triplet (X, Y, Z), such that 0 ≤ X < Y < Z < N, is called a double slice.

The sum of double slice (X, Y, Z) is the total of
A[X + 1] + A[X + 2] + ... + A[Y − 1] + A[Y + 1] + A[Y + 2] + ... + A[Z − 1].

For example, array A such that:

　　A[0] = 3
　　A[1] = 2
　　A[2] = 6
　　A[3] = -1
　　A[4] = 4
　　A[5] = 5
　　A[6] = -1
　　A[7] = 2

contains the following example double slices:

　　double slice (0, 3, 6), sum is 2 + 6 + 4 + 5 = 17,
　　double slice (0, 3, 7), sum is 2 + 6 + 4 + 5 − 1 = 16,
　　double slice (3, 4, 5), sum is 0.

The goal is to find the maximal sum of any double slice.

Write a function:

　　def solution(A)

that, given a non-empty zero-indexed array A consisting of N integers,
returns the maximal sum of any double slice.

For example, given:

　　A[0] = 3
　　A[1] = 2
　　A[2] = 6
　　A[3] = -1
　　A[4] = 4
　　A[5] = 5
　　A[6] = -1
　　A[7] = 2

the function should return 17,
because no double slice of array A has a sum of greater than 17.

Assume that:

N is an integer within the range [3..100,000];
each element of array A is an integer within the range [−10,000..10,000].

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方法一：參考 martinkysel.com 提供的做法
Correctness：100%、Performance：100%

def solution(S):
  length = len(A)
  start = [0] * length
  end = [0] * length

  for i in reversed(range(length-1)):
    start[i] = max(0, start[i+1] + A[i])

  for i in range(1, length):
    end[i] = max(0, end[i-1] + A[i])

  maxDoubleSlice = 0
  for i in range(1, length-1):
  　maxDoubleSlice = max(maxDoubleSlice, start[i+1] + end[i-1])

  return maxDoubleSlice

完整練習題 source code 請參閱：github