hw-02: First implementation

homework-02-rail-building/main.c

@@ -0,0 +1,196 @@
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+#ifdef __PROGTEST__
+#define debug(...) ((void)0)
+#else
+#define debug(fmt, ...)                                                        \
+  fprintf(stdout, "[DEBUG %s:%d %s()] " fmt "\n", __FILE__, __LINE__,          \
+          __func__, ##__VA_ARGS__)
+#endif
+
+typedef long long int lli;
+
+typedef struct rails_t {
+  lli rail_length_1;
+  lli *larger_length;
+  lli rail_length_2;
+  lli *shorter_length;
+  lli total_distance;
+} rails_t;
+
+// find the pivot using the smaller of the rail lengths
+// once pivot is found, the smallest step that will be used is
+// gcd(rail length 1, rail length 2)
+//
+
+int invalid_input() {
+  printf("Nespravny vstup.\n");
+  return EXIT_FAILURE;
+}
+
+// https://www.geeksforgeeks.org/dsa/steins-algorithm-for-finding-gcd/
+int gcd(int a, int b) {
+  if (a == 0)
+    return b;
+  if (b == 0)
+    return a;
+
+  int k;
+  for (k = 0; ((a | b) & 1) == 0; ++k) {
+    a >>= 1;
+    b >>= 1;
+  }
+
+  while ((a & 1) == 0)
+    a >>= 1;
+
+  do {
+    while ((b & 1) == 0)
+      b >>= 1;
+
+    if (a > b) {
+      a ^= b;
+      b ^= a;
+      a ^= b;
+    }
+
+    b = (b - a);
+  } while (b != 0);
+
+  return a << k;
+}
+
+lli find_pivot(rails_t rails) {
+  lli pivot = -1;
+
+  lli current_step;
+
+  lli ratio = (rails.total_distance / *rails.shorter_length);
+
+  for (lli i = 1; i < ratio; i++) {
+    current_step = rails.total_distance - i * (*rails.shorter_length);
+
+    if (current_step % (*rails.larger_length) == 0) {
+      debug("Found pivot %lld\n", i);
+      pivot = i;
+      break;
+    }
+  }
+
+  return pivot;
+}
+
+lli find_smallest_step(rails_t rails) {
+  return *rails.larger_length / gcd(rails.rail_length_1, rails.rail_length_2);
+}
+
+lli find_solutions(rails_t rails, bool verbose) {
+  lli variants = 0;
+
+  lli pivot = find_pivot(rails);
+  lli smallest_step = find_smallest_step(rails);
+  debug("Smallest step = %lld", smallest_step);
+
+  if (pivot != -1) {
+    lli i;
+    for (i = pivot;; i += smallest_step) {
+
+      if ((rails.total_distance - i * (*rails.shorter_length)) < 0) {
+        break;
+      }
+
+      if (verbose) {
+
+        if (*rails.shorter_length == rails.rail_length_1) {
+          printf("= %lld * %lld + %lld * %lld\n", rails.rail_length_1, i,
+                 rails.rail_length_2,
+                 (rails.total_distance - i * rails.rail_length_1) /
+                     rails.rail_length_2);
+        } else {
+          printf("= %lld * %lld + %lld * %lld\n", rails.rail_length_1,
+                 (rails.total_distance - i * rails.rail_length_2) /
+                     rails.rail_length_1,
+                 rails.rail_length_2, i);
+        }
+      }
+
+      variants++;
+    }
+  }
+
+  return variants;
+}
+
+int main() {
+  printf("Delky koleji:\n");
+
+  lli rail_length_1 = -1, rail_length_2 = -1;
+  if (scanf(" %lld %lld", &rail_length_1, &rail_length_2) != 2 ||
+      (rail_length_1 <= 0 && rail_length_2 <= 0) ||
+      (rail_length_1 == rail_length_2)) {
+    return invalid_input();
+  }
+
+  printf("Vzdalenost:\n");
+
+  lli total_distance = 0;
+  char operand;
+
+  if (scanf(" %c %lld", &operand, &total_distance) != 2 ||
+      (operand != '+' && operand != '-')) {
+    return invalid_input();
+  }
+
+  lli variants = 0;
+  bool verbose = operand == '+';
+  if (total_distance < 0) {
+    return invalid_input();
+  }
+  if (total_distance == 0) {
+    if (verbose) {
+      printf("= %lld * 0 + %lld * 0\n", rail_length_1, rail_length_2);
+    }
+    variants++;
+  } else if (rail_length_1 == 0 && total_distance % rail_length_2 == 0) {
+    if (verbose) {
+      printf("= %lld * %lld + %lld * 0\n", rail_length_1,
+             total_distance / rail_length_2, rail_length_2);
+    }
+  } else if (rail_length_2 == 0 && total_distance % rail_length_1 == 0) {
+    if (verbose) {
+      printf("= %lld * 0 + %lld * %lld\n", rail_length_1, rail_length_2,
+             total_distance / rail_length_1);
+    }
+  } else if (rail_length_1 > 0 && rail_length_2 > 0) {
+
+    lli *smaller =
+        rail_length_1 > rail_length_2 ? &rail_length_2 : &rail_length_1;
+    lli *larger =
+        rail_length_1 > rail_length_2 ? &rail_length_1 : &rail_length_2;
+
+    rails_t rails;
+    rails.rail_length_1 = rail_length_1;
+    rails.rail_length_2 = rail_length_2;
+    rails.total_distance = total_distance;
+    rails.shorter_length = smaller;
+    rails.larger_length = larger;
+
+    if (total_distance % rail_length_1 == 0) {
+      if (verbose) {
+        printf("= %lld * %lld + %lld * 0\n", rail_length_1,
+               total_distance / rail_length_1, rail_length_2);
+      }
+      variants++;
+    }
+
+    variants += find_solutions(rails, verbose);
+  }
+
+  if (variants != 0) {
+    printf("Celkem variant: %lld\n", variants);
+  } else {
+    printf("Reseni neexistuje.\n");
+  }
+}