77 lines
1.8 KiB
C
77 lines
1.8 KiB
C
#include <stdlib.h>
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// 定义点结构
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typedef struct {
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int x;
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int y;
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} Point;
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// 计算叉积
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double crossProduct(Point p0, Point p1, Point p2) {
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return (p1.x - p0.x) * (p2.y - p0.y) - (p2.x - p0.x) * (p1.y - p0.y);
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}
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// 计算两点间距离的平方
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double distanceSquare(Point p1, Point p2) {
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return (p1.x - p2.x) * (p1.x - p2.x) + (p1.y - p2.y) * (p1.y - p2.y);
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}
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// 比较函数
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Point p0;
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int comparePoints(const void* vp1, const void* vp2) {
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Point* p1 = (Point*)vp1;
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Point* p2 = (Point*)vp2;
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double cross = crossProduct(p0, *p1, *p2);
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if (cross == 0) {
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return (distanceSquare(p0, *p1) - distanceSquare(p0, *p2));
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}
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return (cross < 0) ? 1 : -1;
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}
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// 导出的凸包计算函数
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void convexHull(Point* points, int n, Point* result, int* resultSize) {
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if (n < 3) {
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// 点数小于3，直接复制所有点
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for (int i = 0; i < n; i++) {
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result[i] = points[i];
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}
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*resultSize = n;
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return;
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}
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// 找到y坐标最小的点
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int min = 0;
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for (int i = 1; i < n; i++) {
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if (points[i].y < points[min].y ||
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(points[i].y == points[min].y && points[i].x < points[min].x)) {
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min = i;
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}
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}
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// 将最下方的点交换到points[0]
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Point temp = points[0];
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points[0] = points[min];
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points[min] = temp;
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// 保存最下方的点用于排序
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p0 = points[0];
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// 按极角排序
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qsort(&points[1], n-1, sizeof(Point), comparePoints);
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// 构建凸包
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int m = 0;
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result[m++] = points[0];
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result[m++] = points[1];
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result[m++] = points[2];
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for (int i = 3; i < n; i++) {
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while (m > 1 && crossProduct(result[m-2], result[m-1], points[i]) <= 0) {
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m--;
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}
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result[m++] = points[i];
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}
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*resultSize = m;
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}
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