42 lines
1.1 KiB
C
42 lines
1.1 KiB
C
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#include <stdlib.h>
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// 定义一个点结构体
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typedef struct {
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int x, y;
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} Point;
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// 计算两点的极角
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int orientation(Point p, Point q, Point r) {
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int val = (q.y - p.y) * (r.x - q.x) - (q.x - p.x) * (r.y - q.y);
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if (val == 0) return 0; // 共线
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return (val > 0) ? 1 : 2; // 顺时针或逆时针
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}
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// 对点的极角排序
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int compare(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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return (p1->y < p2->y) || (p1->y == p2->y && p1->x < p2->x);
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}
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// 凸包主函数
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void convexHull(Point points[], int n, Point result[], int *result_size) {
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// 如果点数小于 3，无法构成凸包
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if (n < 3) {
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*result_size = 0;
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return;
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}
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// 按 y 坐标排序，如果 y 坐标相同则按 x 坐标排序
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qsort(points, n, sizeof(Point), compare);
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// 构建凸包
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int m = 0; // 凸包的点数
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for (int i = 0; i < n; i++) {
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while (m >= 2 && orientation(result[m-2], result[m-1], points[i]) != 2)
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m--;
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result[m++] = points[i];
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}
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*result_size = m;
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}
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