def MaxCrossSubarray(num,mid,low,high):
leftsum=0
leftmax=-1000000
rightsum=0
rightmax=-1000000
for i in range(mid,low-1,-1):
leftsum=leftsum+num[i]
if leftsum>leftmax:
leftmax=leftsum
leftlow=i
for j in range(mid+1,high+1):
rightsum=rightsum+num[j]
if rightsum>rightmax:
rightmax=rightsum
righthigh=j
sum=leftmax+rightmax
return (leftlow,righthigh,sum)
def MaxSubarray(num,low,high):
if low==high:
return (low,high,num[low])
else:
mid=(low+high)//2
(left_low,left_high,left_sum)=MaxSubarray(num,low,mid)
(right_low,right_high,right_sum)=MaxSubarray(num,mid+1,high)
(cross_low,cross_high,cross_sum)=MaxCrossSubarray(num,mid,low,high)
if(left_sum>right_sum and left_sum>cross_sum):
return (left_low,left_high,left_sum)
elif(right_sum>left_sum and right_sum>cross_sum):
return (right_low,right_high,right_sum)
elif(cross_sum>left_sum and cross_sum>right_sum):
return (cross_low,cross_high,cross_sum)
a=[13, -3, -25, 20, -3, -16, -23, 18, 20, -7, 12, -5, -22, 15, -4, 7]
max = MaxSubarray(a, 0, len(a)-1)
print max
