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  1. #include <stdio.h>
  2.  
  3. struct point2d {                /* 2次元空間の点のx座標とy座標をそれぞれdoubleに格納 */
  4.     double x, y;
  5. };
  6.  
  7. struct linesegment {            /* 線分の始点sと終点eをそれぞれstruct point2dに格納 */
  8.     struct point2d s, e;
  9. };
  10.  
  11. /* 交点判定 (1:交わる、0:交わらない) */
  12. int if_intersect(struct linesegment line1, struct linesegment line2)
  13. {
  14.     double m[2];                /* 傾き                 */
  15.     int f_mv[2];                /* y軸と平行かのフラグ  */
  16.     struct point2d kt;          /* 交点                 */
  17.  
  18.     /* 傾き */
  19.     f_mv[0] = (line1.e.x == line1.s.x) ? 1 : 0;
  20.     if (f_mv[0] == 0) {
  21.         m[0] = (line1.e.y - line1.s.y) / (line1.e.x - line1.s.x);
  22.     }
  23.     f_mv[1] = (line2.e.x == line2.s.x) ? 1 : 0;
  24.     if (f_mv[1] == 0) {
  25.         m[1] = (line2.e.y - line2.s.y) / (line2.e.x - line2.s.x);
  26.     }
  27.     /* 平行か？ */
  28.     if (f_mv[0] == 1 && f_mv[1] == 1) {
  29.         return 0;
  30.     }
  31.     if (f_mv[0] == 0 && f_mv[1] == 0) {
  32.         if (m[0] == m[1]) {
  33.             return 0;
  34.         }
  35.     }
  36.     /* 交点計算 */
  37.     if (f_mv[0] == 0 && f_mv[1] == 0) {
  38.         kt.x = (m[0] * line1.s.x - line1.s.y - m[2] * line2.s.x + line2.s.y) / (m[0] - m[1]);
  39.         kt.y = m[0] * kt.x - m[0] * line1.s.x + line1.s.y;
  40.     } else if (f_mv[0]) {
  41.         kt.x = line1.s.x;
  42.         kt.y = m[1] * line1.s.x - m[1] * line2.s.x + line2.s.y;
  43.     } else if (f_mv[1]) {
  44.         kt.x = line2.s.x;
  45.         kt.y = m[0] * line2.s.x - m[0] * line1.s.x + line1.s.y;
  46.     }
  47.     /* 交点が線分の範囲内か判定 */
  48.     if (f_mv[0]) {
  49.         if (line1.s.y < line1.e.y) {
  50.             if (line1.s.y <= kt.y && kt.y <= line1.e.y) {
  51.                 return 1;
  52.             }
  53.         } else {
  54.             if (line1.e.y <= kt.y && kt.y <= line1.s.y) {
  55.                 return 1;
  56.             }
  57.         }
  58.     }
  59.     if (f_mv[1]) {
  60.         if (line2.s.y < line2.e.y) {
  61.             if (line2.s.y <= kt.y && kt.y <= line2.e.y) {
  62.                 return 1;
  63.             }
  64.         } else {
  65.             if (line2.e.y <= kt.y && kt.y <= line2.s.y) {
  66.                 return 1;
  67.             }
  68.         }
  69.     }
  70.     return 0;
  71. }
  72.  
  73. /*  main        */
  74. int main()
  75. {
  76.     struct linesegment line1 = {
  77.         {0.0, 0.0},
  78.         {2.0, 1.0}
  79.     };
  80.     struct linesegment line2 = {
  81.         {1.0, 2.0},
  82.         {1.0, 0.6}
  83.     };
  84.  
  85.     printf(
  86.         "線分 [%f, %f]-[%f, %f]\n"
  87.         "と   [%f, %f]-[%f, %f]\n"
  88.         "は、交わ%s\n"
  89.         , line1.s, line1.e, line2.s, line2.e
  90.         , if_intersect(line1, line2) ? "る" : "らない"
  91.     );
  92.     return 0;
  93. }
  94.  
Success #stdin #stdout 0s 1832KB
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Standard input is empty
stdout
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線分 [0.000000, 0.000000]-[2.000000, 1.000000]
と   [1.000000, 2.000000]-[1.000000, 0.600000]
は、交わらない
https://ideone.com/wHWliE
language:
C (gcc 8.3)
created:
11 years ago
visibility:
public

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