poj-1314 Finding Rectangles

#include <cstdio>  
#include <iostream>
#include <cstring> 
#include <cstdlib> 
#include <string> 
#include <cmath> 
#include <vector> 
#include <algorithm> 
using namespace std; 
const int maxn = 30; 

struct Node{
	string label; 
	int x,y; 
}nd[maxn]; 

int n; 

int cmp(const void *a, const void *b){
	Node* aa = (Node *)a; 
	Node* bb = (Node *)b; 
	if(aa->x == bb->x){
		return aa->y - bb->y; 
	}else{
		return aa->x - bb->x; 
	}
}

int main(){
	freopen("in.txt", "r", stdin); 

	int i,j,k, l, cnt = 1; 
	char word[4]; 
	while( cin>>n && n!=0){
		for(i=0; i<n; i++){
			cin>>nd[i].label>>nd[i].x>>nd[i].y;  
		}
		qsort(nd, n, sizeof(nd[0]), cmp); 
		vector<string> vt; 
		for(i=0; i<n; i++){
			for(j=i+1; j<n && nd[j].x == nd[i].x; j++){
				for(k=j+1; k<n; k++){
					if(nd[k].y == nd[i].y){
						for(l=k+1; l<n && nd[l].x == nd[k].x; l++){
							if(nd[l].y == nd[j].y){
								string tmp = ""; 
								tmp += nd[j].label;  tmp += nd[l].label; 
								tmp += nd[k].label;  tmp += nd[i].label;
								vt.push_back(tmp); 
							}
						}
					}
				}
			}
		}
		if(vt.size() == 0){
			printf("Point set %d: No rectangles\n", cnt++);
		}else{
			printf("Point set %d:\n", cnt++);
			sort(vt.begin(), vt.end()); 
			for(i=0; i<vt.size(); i++){
				if((i+1)%10 == 0){
					cout<<" "<<vt[i]<<endl;
				}else{
					cout<<" "<<vt[i]; 
				}
			}
			if(i%10 != 0){
				printf("\n");
			}
		}
	}
	return 0; 
}