3664-顺序表应用7：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;
}