最大子数组问题的分治算法

#include <iostream>
#include <algorithm>
#include <vector>
using namespace std;


/*最大子数组问题的分治算法*/
#define INT32_MIN (1<<29)

/*
* find a subarray crossing the mid with the biggist sum
*/
int find_max_crossing_subarray(vector<int> array, int low, int mid, int high)
{
	int left_maxsum = -50; //for sum
	int right_maxsum = -50; //for sum
	int sum = 0;
	for (int i = mid; i >= low; --i)
	{
		sum += array[i];
		if (sum > left_maxsum)
		{
			left_maxsum = sum;

		}
	}

	sum = 0;
	for (int i = mid + 1; i <= high; ++i)
	{
		sum += array[i];
		if (sum > right_maxsum)
		{
			right_maxsum = sum;

		}
	}
	return(left_maxsum + right_maxsum);

	//cout<<"maxsum_crossing_mid"<<left_maxsum+right_maxsum<<endl;
}

int max(int a, int b, int c)
{
	if (a >= b && a >= c)
		return a;
	else if (b >= a && b >= c)
		return b;
	else
		return c;
}
/*
* find a subarray on the left or right side of mid
*/
int find_max_subarray(vector<int> array, int low, int high)
{
	if (low == high)
	{
		return array[low];
	}
	int mid = int((low + high) / 2);
	int low_maxsum = find_max_subarray(array, low, mid);
	int high_maxsum = find_max_subarray(array, mid + 1, high);
	int crossing_mid_maxsum = find_max_crossing_subarray(array, low, mid, high);
	return max(low_maxsum, high_maxsum, crossing_mid_maxsum);
}
int main()
{
	vector<int> array;
	for (int i = 0; i<10; i++)
	{
		int j = 50 - rand() % 100; //-49~50
		array.push_back(j);
	}

	for (vector<int>::iterator it = array.begin(); it != array.end(); ++it)
	{
		cout << *it << " ";
	}
	cout << endl;
	int maxsum = find_max_subarray(array, 0, array.size() - 1);
	cout << "the maxsum=" << maxsum << endl;

	return 0;
}