zoj 3574 求给定区间内n条线段能将区间内的区域划分成几个区域

#include <cstdio>
#include <algorithm>
using namespace std;
int left[50003], right[50003];
int cnt;
struct node {
int y1,y2;
}p[30010];
int cmp(node a,node b){
return a.y1<b.y1;
}
void merge(int a[], int l, int m, int r)  {
int i, j, k, n1, n2;
n1 = m - l + 1;
n2 = r - m;
for (i = 0; i < n1; i++)
left[i] = a[l+i];
for (i = 0; i < n2; i++)
right[i] = a[m+i+1];
left[n1] = right[n2] = 0x7fffffff;
i = j = 0;
for (k = l; k <= r; k++)  {
if (left[i] <= right[j])   a[k] = left[i++];
else  {
a[k] = right[j++];
cnt += n1 - i;
}
}
}
void mergeSort(int a[], int l, int r)  {
if (l < r)  {
int m = (l + r) / 2;
mergeSort(a, l, m);
mergeSort(a, m+1, r);
merge(a, l, m, r);
}
}
int  a[50011];
int main()  {
int n;
int l,r;
while (scanf("%d%d",&l,&r)!=EOF)  {
scanf("%d",&n);
int k,b;
for(int i=0;i<n;i++){
scanf("%d%d",&k,&b);
p[i].y1=k*l+b;
p[i].y2=k*r+b;
}
sort(p,p+n,cmp);
for(int i=0;i<n;i++)        a[i]=p[i].y2;
cnt=0;mergeSort(a, 0, n-1);
printf("%d\n", n+cnt+1);
}
}