返回错误输出的最大和子数组

Posted 2023-03-27

【中文标题】返回错误输出的最大和子数组

【英文标题】：Maximum sum subarray returning wrong output

【发布时间】：2017-11-05 20:52:52

【问题描述】：

算法看起来正确，但无法找出错误所在。从 8 到 10 返回的代码是最大子数组，共 32 个。但实际答案是 8 到 11，共 43 个。

import sys
import math

def maxtuple(lss,rss):
  if lss[2] > rss[2]:
      return lss
  else:
      return rss

def crosssubarray(A, start, mid, end):
  ls=rs=-sys.maxsize
  maxleft=0
  maxright=0
  sum = 0;
  for i in reversed(range(start, mid)):
    sum = sum + A[i]
    print(i)
    if sum > ls:
        ls = sum
        maxleft = i
  sum = 0
  for i in range(mid+1, end):
    sum = sum+ A[i]
    if sum > rs:
        rs = sum
        maxright = i
  return (maxleft, maxright, ls+rs)

def maxsubarray(A,start,end):
  if start == end:
    return (start,end,A[start])
  else:
    mid = (start+end)/2
    lss = maxsubarray(A, start, mid)
    rss = maxsubarray(A, mid+1, end)
    css = crosssubarray(A, start, mid, end)
    maxsub = maxtuple(lss,rss)
    maxall = maxtuple(maxsub, css)
    return maxall`enter code here`

A = [13,-3,-25,20,-3,-16,-23,18,20,-7,12,-5,-22,15,-4,7]
print(maxsubarray(A,0,15))

【问题讨论】：

抱歉，实际输出应该是 7 到 10 共 43 个

【参考方案1】：

问题是 range(start, mid) 产生 start,start+1,..,mid-1 但不包括 mid。

这意味着您的交叉子数组不包含中间值。

改为尝试：

for i in reversed(range(start, mid+1)):