【CodeForces】[621B]Wet Shark and Bishops

#include<stdio.h>
#include<string.h>
int a[2020],b[2020];
int main() {
int n;
while(scanf("%d",&n)!=EOF) {
memset(a,0,sizeof(a));
memset(b,0,sizeof(b));
for(int i=0; i<n; i++) {
int x,y;
scanf("%d %d",&x,&y);
if(x>y)
a[1000+x-y]++;
else
a[y-x]++;
b[x+y]++;
}
int res=0;
for(int i=0; i<2020; i++) {
if(a[i]) {
res+=(a[i]-1)*a[i]/2;
}
if(b[i]) {
res+=(b[i]-1)*b[i]/2;
}
}
printf("%d\n",res);
}
return 0;
}