最大子序列-NlogN

//分治
#include<iostream>
using namespace std;
int MaxSubSum(int A[], int Left, int Right)
{
int MaxLeftSum, MaxRightSum;
int MaxLeftBorderSum, MaxRightBorderSum;
int LeftBorderSum, RightBorderSum;
int Center;
if(Left == Right)
{
if(A[Left] > 0)
{
return A[Left];
}
else
{
return 0;
}
}

Center = (Left + Right)/2;
MaxLeftSum = MaxSubSum(A, Left, Center);
MaxRightSum = MaxSubSum(A, Center+1, Right);
MaxLeftBorderSum = LeftBorderSum = 0;
for(int i = Center; i >= Left; --i)
{
LeftBorderSum += A[i];
if(LeftBorderSum > MaxLeftBorderSum)
{
MaxLeftBorderSum = LeftBorderSum;
}
}
MaxRightBorderSum = RightBorderSum = 0;
for(int i = Center+1; i <= Right; ++i)
{
RightBorderSum += A[i];
if(RightBorderSum > MaxRightBorderSum)
{
MaxRightBorderSum = RightBorderSum;
}
}
if(MaxLeftSum > MaxRightSum)
{
if(MaxLeftSum > (MaxLeftBorderSum+MaxRightBorderSum))
return MaxLeftSum;
else
return MaxLeftBorderSum+MaxRightBorderSum;
}
else
{
return (MaxRightSum > (MaxRightBorderSum+MaxLeftBorderSum))?MaxRightSum:(MaxLeftBorderSum+MaxRightBorderSum);
}
}
int main()
{
int A[] = {4, -3, 5, -2, -1, 2, 6, -2};
cout<<MaxSubSum(A, 0, 7);
}