USACO 3.1.3 – Shaping Regions

For each new rectangle layer; check the intersection with all previous rectangles which were not cut, divide the rectangle into 4 regions.

  • first case is obvious
  • for all other cases of intersection some of the rectangles will have area 0 being found at the edges of the older rectangle.
    • and thus won’t be calculated.

after cutting a previous layer, mark it as torn so that it won’t be checked for intersection later.

#include <cstdio>
#include <algorithm>
using namespace std;

struct Rectangle { int ax, ay, bx, by, c; } rec[100001];
int main() {
	freopen("", "r", stdin), freopen("rect1.out", "w", stdout);
	int W, H, N, top=0, cut[100000]= {0}, count[2501]={0}, ax, ay, bx, by, c;
	scanf("%d %d %d", &W, &H, &N);

	rec[top++] = Rectangle {0,0,W,H,1};
	for(int i=0; i<N; ++i){
		scanf("%d %d %d %d %d", &ax, &ay, &bx, &by, &c);
		rec[top++]= Rectangle{ax, ay, bx, by, c};
		for(int j=0, J=top-1; j<J; ++j)
				int max_ax = max(ax, rec[j].ax), max_ay = max(ay, rec[j].ay);
				int min_bx = min(bx, rec[j].bx), min_by = min(by, rec[j].by);
				if(max_ax >= min_bx || max_ay >= min_by) continue; else cut[j]++;
				rec[top++] = Rectangle { rec[j].ax, rec[j].ay, min_bx   , max_ay   , rec[j].c};
				rec[top++] = Rectangle { min_bx	  , rec[j].ay, rec[j].bx, min_by   , rec[j].c};
				rec[top++] = Rectangle { rec[j].ax, max_ay 	 , max_ax   , rec[j].by, rec[j].c};
				rec[top++] = Rectangle { max_ax	  , min_by	 , rec[j].bx, rec[j].by, rec[j].c};
	for(int i=0; i<top; ++i)
			count[rec[i].c] += (rec[i].bx- rec[i].ax)*(rec[i].by- rec[i].ay);

	for(int i=1; i<=2500; ++i)
			printf("%d %d\n", i, count[i]);

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