hdu1255(线段树求面积交)

来源：互联网发布：淘宝电棍编辑：程序博客网时间：2024/05/17 01:48

和Poj1151线段树求面积并的原理相同

不同的地方：至少覆盖一次one和至少覆盖两次two的更新

注意点：

1、由于没有push_down的操作，当父节点的cover==1,子节点的cover也等于1，则父节点的two要更新

当父节点的over==0，子节点的cover=1，父节点的one要更新

子节点的cover=2，父节点的two要更新

2、由于是左闭有开区间，而我们记录的是线段，当l+1==r时注意返回

代码

#pragma warning(disable:4996)#include <stdio.h>#include <algorithm>using namespace std;const int maxn = 1005 * 2;struct node{int l, r, cover;double ly, ry, one, two;}segTree[maxn * 3];struct line{double x, y1, y2;int tag;bool operator < (const line& l)const {return x<l.x;}}lines[maxn];double y[maxn];void build(int i, int l, int r){segTree[i].l = l;segTree[i].r = r;segTree[i].cover = 0;segTree[i].one = 0;segTree[i].two = 0;segTree[i].ly = y[l];segTree[i].ry = y[r];if (l + 1 == r)return;int mid = (l + r) / 2;build(i << 1, l, mid);build(i << 1 | 1, mid, r);}void cal(int i){if (segTree[i].cover >= 2){segTree[i].two = segTree[i].ry - segTree[i].ly;}else if (segTree[i].cover == 1){segTree[i].one = segTree[i].ry - segTree[i].ly;if (segTree[i].l + 1 == segTree[i].r)segTree[i].two = 0;else segTree[i].two = segTree[i << 1].one + segTree[i << 1 | 1].one;}else{if (segTree[i].l + 1 == segTree[i].r){segTree[i].one = segTree[i].two = 0;}else{segTree[i].one = segTree[i << 1].one + segTree[(i << 1) | 1].one;segTree[i].two = segTree[i << 1].two + segTree[(i << 1) | 1].two;}}}void update(int i, line&l){if (l.y1 == segTree[i].ly&&l.y2 == segTree[i].ry){segTree[i].cover += l.tag;cal(i);return;}if (l.y2 <= segTree[i << 1].ry)update(i << 1, l);else if (l.y1 >= segTree[i << 1 | 1].ly)update(i << 1 | 1, l);else{double tmpy = l.y2;l.y2 = segTree[i << 1].ry;update(i << 1, l);l.y2 = tmpy;tmpy = l.y1;l.y1 = segTree[i << 1 | 1].ly;update(i << 1 | 1, l);l.y1 = tmpy;}cal(i);}int main(){//freopen("in.txt", "r", stdin);int n, T, tot ;double x1, y1, x2, y2;scanf("%d", &T);while (T--){tot = 1;scanf("%d", &n);for (int i = 0; i<n; i++){scanf("%lf %lf %lf %lf", &x1, &y1, &x2, &y2);lines[tot].x = x1;lines[tot].y1 = y1;lines[tot].y2 = y2;lines[tot].tag = 1;y[tot] = y1;tot++;lines[tot].x = x2;lines[tot].y1 = y1;lines[tot].y2 = y2;lines[tot].tag = -1;y[tot] = y2;tot++;}sort(lines + 1, lines + tot);sort(y + 1, y + tot);build(1, 1, tot - 1);update(1, lines[1]);double area = 0.0;for (int i = 2; i<tot; i++){area += segTree[1].two*(lines[i].x - lines[i - 1].x);update(1, lines[i]);}printf("%.2lf\n", area);}return 0;}

0 0