分治策略-最大子数组问题

#include<iostream>
#include<algorithm>
#define INFO -999999
#include<math.h>
using namespace std;

typedef struct array1 {
int low;
int mid;
int high;
};

struct array1 find_max_crossing(struct array1 *a,int A[]) {
static struct array1 sum1;
int left_sum = INFO;
int sum = 0, i;
int max_left;
for (i = a->mid; i >= a->low; --i) {
sum += A[i];
if (sum > left_sum) {
left_sum = sum;
max_left = i;
}
}
sum1.low = max_left;
int right_sum = INFO;
sum = 0;
int j;
int max_right;
for (j = a->mid + 1; j <= a->high; ++j) {
sum += A[j];
if (sum > right_sum) {
right_sum = sum;
max_right = j;
}
}
sum1.high = max_right;
sum1.mid = max_left + max_right;
return sum1;
}

struct array1 find_maximum_subarray(int A[], int low, int high) {
static struct array1 result[4];
struct array1 *a;
a->low = low;
a->high = high;
a->mid = floor((low + high) / 2);
if (high == low) {
result[0].low = low;
result[0].high = high;
result[0].mid = A[low];
return result[0];
}
else {
int mid1 = floor((low + high) / 2);
result[1] = find_maximum_subarray(A, low, mid1);
result[2] = find_maximum_subarray(A, mid1 + 1, high);
result[3] = find_max_crossing(a, A);
if (result[1].mid >= result[2].mid&&result[1].mid >= result[3].mid)
return result[1];
else if (result[2].mid >= result[1].mid&&result[2].mid >= result[3].mid)
return result[2];
else
return result[3];
}

}