HDU1542矩形面积并

取出纵向边按x坐标排序，在y方向上建立线段树。

每次查询当前有效长度len，ans += len*(x[i]-x[i-1]); 其中len为T[rt].len;

查询完毕后更新y方向上线段树，入边+1，出边-1。

 1 #include<bits/stdc++.h>
 2 using namespace std;
 3 #define lson l, m, rt<<1
 4 #define rson m+1, r, rt<<1|1
 5 typedef long long ll;
 6 struct L{
 7     double x, y1, y2;
 8     int d;
 9     L(){}
10     L(double x, double y1, double y2, int d): x(x), y1(y1), y2(y2), d(d){}
11 };
12 L line[500];
13 bool cmp(L A, L B){
14     return A.x < B.x;
15 }
16 double y[500];
17 
18 struct Node{
19     int d;
20     double len;
21 };
22 Node T[500<<3];
23 void init(){
24     memset(T, 0, sizeof(T));
25 }
26 void pushup(int rt, int l, int r){
27     if(T[rt].d)
28         T[rt].len = y[r]-y[l-1];
29     else
30         T[rt].len = l == r? 0 : T[rt<<1].len+T[rt<<1|1].len;
31 }
32 void update(int L, int R, int d, int l, int r, int rt){
33     if(L <= l&&r <= R){
34         T[rt].d += d;
35         pushup(rt, l , r);
36         return ;
37     }
38     int m = (l+r)>>1;
39     if(L <= m) update(L, R, d, lson);
40     if(R > m) update(L, R, d, rson);
41     pushup(rt, l, r);
42 }
43 
44 int main(){
45     int n, ca = 1;
46     double x1, y1, x2, y2;
47     while(scanf("%d", &n), n){
48         for(int i = 0; i < n; i++){
49             scanf("%lf%lf%lf%lf", &x1, &y1, &x2, &y2);
50             line[i*2] = L(x1, y1, y2, 1);
51             line[i*2+1] = L(x2, y1, y2, -1);
52             y[i*2] = y1, y[i*2+1] = y2;
53         }
54         sort(line, line+2*n, cmp);
55         sort(y, y+2*n);
56 
57         init();
58         double ans = 0;
59         for(int i = 0; i < 2*n; i++){
60             if(i&&line[i].x != line[i-1].x)
61                 ans += (line[i].x-line[i-1].x)*T[1].len;
62             int l = lower_bound(y, y+2*n, line[i].y1)-y+1, r = lower_bound(y, y+2*n, line[i].y2)-y;
63             if(l <= r)
64                 update(l, r, line[i].d, 1, 2*n, 1);
65         }
66         printf("Test case #%d\n", ca++);
67         printf("Total explored area: %.2f\n\n", ans);
68     }
69     return 0;
70 }

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