最大子段和之分治递归法

#include<stdio.h>
#include<algorithm>
#include<iostream>
#include<string.h>
using namespace std;
const int MAX = 50000+10;
int maxx, cnt, n, a[MAX];
int maxsum(int l, int r)
{
	int sum = 0;
	cnt++;
	if(l==r)
	{
		if(a[l]>=0)sum = a[l];
		else sum = 0;
	}
	else
	{
		int mid = (l+r)/2;
		int leftsum = maxsum(l, mid);
		int rightsum = maxsum(mid+1, r);
		int s1, s2, ss;
		s1 = ss = 0;
		for(int i = mid; i>=l; --i)
		{
			ss+=a[i];
			if(ss>s1)s1 = ss;
		}
		s2 = ss = 0;
		for(int i = mid+1; i<=r; ++i)
		{
			ss+=a[i];
			if(ss>s2)s2 = ss;
		}
		sum = s1+s2;
		sum = max(sum, leftsum);
		sum = max(sum, rightsum);
	}
	return sum;
}

int main()
{
    scanf("%d",&n);
    for(int i = 0; i<n; ++i)
		scanf("%d", &a[i]);
    cnt = 0;
    maxx = maxsum(0, n-1);
    printf("%d %d\n", maxx, cnt);
    return 0;
}