poj 1788 Building a New Depot

#include<cstdio>#include<cstring>#include<algorithm>using namespace std;struct data{    int x,y;}po[101000];bool compx(data a,data b){    return (a.x!=b.x)?a.x<b.x:a.y<b.y;}bool compy(data a,data b){    return (a.y!=b.y)?a.y<b.y:a.x<b.x;}int main(){    int n;    while(scanf("%d",&n),n)    {        for(int i=0;i<n;i++) scanf("%d%d",&po[i].x,&po[i].y);        int ans=0;        sort(po,po+n,compx);        for(int i=0;i<n-1;i+=2) ans+=po[i+1].y-po[i].y;        sort(po,po+n,compy);        for(int i=0;i<n-1;i+=2) ans+=po[i+1].x-po[i].x;        printf("The length of the fence will be %d units.n",ans);    }    return 0;}