最大子阵列程序实现未终止

我正在尝试实现使用分而治技术在数组中查找最大子数组总和的算法，但由于某种原因，程序没有终止，我没有设法自己成功调试它。有人可以告诉我问题出在哪里吗？

#include <iostream>
#include <cmath>
using namespace std;
int max_sub_arr(int arr[], int beginning, int end);
int helper_sub_arr(int arr[], int left, int center, int right);
int a[15] = {5, -2, 5, -6, 8, 20, -15, 4, 5, 3, -1, -2 , -5, 10, 1};
int length = 15;
int main()
{
    cout <<max_sub_arr(a, 0, length-1) << endl;
    return 0;
}
int max_sub_arr(int arr[], int beginning, int end)
{
    if(beginning == end) return arr[beginning];
    int center = (end - beginning)/2;
    int left = max_sub_arr(arr, beginning, center);
    int right = max_sub_arr(arr, center+1,end);
    int cross = helper_sub_arr(arr, left, center, right);
    if(left >= right && left >= cross) return left;
    else if(right >= left && right >= cross) return right;
    else return cross;
}
int helper_sub_arr(int arr[], int left, int center, int right)
{
    cout<<"as";
    int leftsum = -pow(2, 31);
    int rightsum = -pow(2, 31);
    int sum = 0;
    int maxleft, maxright;
    for(int i = center; i >= 0; --i)
    {
        sum += arr[i];
        if(sum > leftsum)
        {
            leftsum = sum;
            maxleft = i;
        }
    }
    sum = 0;
    for(int i = center + 1; i <= right; ++i)
    {
        sum += arr[i];
        if(sum > rightsum)
        {
            sum = rightsum;
            maxright = i;
        }
    }
    return maxleft + maxright;
}