HDU 1542/POJ 1151 Atlantis (scaning line + segment tree)

A template of discretization + scaning line + segment tree.
It's easy to understand, but a little difficult for coding as it has a few details.

#include"Head.cpp"

const int N=207;

double x[N<<1];

struct Point{
	double l,r,h;
	int w;
	bool operator< (const Point &b)const{
		return h < b.h;
	}
}a[N<<2];

struct SegmentTree{
	int l,r,w;
	double len;
}t[N<<3];


#define lson rt<<1, l, mid
#define rson rt<<1|1, mid+1, r

inline void Pushup(int rt){
	if(t[rt].w != 0)
		t[rt].len = x[t[rt].r+1] - x[t[rt].l];
	else if(t[rt].l == t[rt].r)
		t[rt].len = 0;
	else // t[rt].w == 0
		t[rt].len = t[rt<<1].len + t[rt<<1|1].len;
}

inline void Build(int rt,int l,int r){
	t[rt] = (SegmentTree){l, r, 0, 0};
	if(l == r) return;
	int mid = (l>>1) + (r>>1) + (l&r&1);
	Build(lson),Build(rson);
}

inline void Updata(int rt,int L,int R,int val){
	if(t[rt].l >= L && t[rt].r <= R){
		t[rt].w += val;
		Pushup(rt);
		return;
	}
	int mid = (t[rt].l>>1) + (t[rt].r>>1) +(t[rt].l&t[rt].r&1);
	if(L <= mid) Updata(rt<<1, L, R, val);
	if(R > mid) Updata(rt<<1|1, L, R, val);
	Pushup(rt);
}

inline int FindPos(int l,int r,double val){
	int mid;
	while(l<=r){
		mid = (l>>1) + (r>>1) + (l&r&1);
		if(x[mid] > val)
			r = mid - 1;
		else if(x[mid] < val)
			l = mid + 1;
		else // x[mid] == val
			break;
	}
	return mid;
}

int main(){
	int task=0;
	int n;
	while(~scanf("%d",&n) && n!=0){
		int cnt=0;
		
		R(i,1,n){
			double x_1,x_2,y_1,y_2;
			scanf("%lf%lf%lf%lf",&x_1,&y_1,&x_2,&y_2);
			
			// 1 -> floor, -1 -> ceiling
			x[++cnt] = x_1;
			a[cnt] = (Point){x_1, x_2, y_1, 1};
			x[++cnt] = x_2;
			a[cnt] = (Point){x_1, x_2, y_2, -1};
		}
		
		sort(x+1, x+cnt+1);
		sort(a+1, a+cnt+1);
		Build(1, 1, cnt);
		
		double ans = 0;
		R(i,1,cnt-1){
			int l = FindPos(1, cnt, a[i].l),
				r = FindPos(1, cnt, a[i].r) - 1;
			Updata(1, l, r, a[i].w);
			ans += t[1].len * (a[i+1].h - a[i].h);
		}
		
		printf("Test case #%d\nTotal explored area: %.2lf\n\n", ++task, ans);
	}
	
	return 0;
}
/*
2
10 10 20 20
15 15 25 25.5
0
*/