Activity select problem solved with greedy algorithms (#1901)

greedy_algorithms/activity_select/activity-select-main.c

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+#include <stdio.h>
+
+#include <greedy-algorithms/activity-select/activity-select.h>
+#include <util/list.h>
+
+
+int main() {
+  int s[] = {0, 1, 3, 0, 5, 3, 5,  6,  8,  8,  2, 12};
+  int f[] = {0, 4, 5, 6, 7, 9, 9, 10, 11, 12, 14, 16};
+  size_t s_len = sizeof s / sizeof *s;
+
+  list_t *(*selects[])(int *, int *, size_t) =
+      { recursive_activity_select, iterative_activity_select };
+  size_t selects_len = sizeof selects / sizeof *selects;
+
+  for(size_t i = 0; i < selects_len; i++) {
+    size_t calls = 0;
+    list_t *solution = selects[i](s, f, s_len);
+    list_print(solution);
+    list_destroy(solution);
+  }
+}

greedy_algorithms/activity_select/activity-select.c

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+#include <greedy-algorithms/activity-select/activity-select.h>
+
+
+void recursive_activity_select_aux(int *s, int *f, size_t k, size_t n, list_t *res);
+
+list_t *recursive_activity_select(int *s, int *f, size_t n) {
+  list_t *A = list_init();
+
+  recursive_activity_select_aux(s, f, 0, n, A);
+
+  return A;
+}
+
+void recursive_activity_select_aux(int *s, int *f, size_t k, size_t n, list_t *res) {
+  size_t m = k + 1;
+  while(m <= n && s[m] < f[k]) m++;
+  if (m <= n) {
+    list_add(res, (long)m);
+    recursive_activity_select_aux(s, f, m, n, res);
+  }
+}
+
+list_t *iterative_activity_select(int *s, int *f, size_t n) {
+  list_t *A = list_init();
+
+  size_t k = 1;
+  list_add(A, 1);
+  for(size_t m = 2; m < n; ++m) {
+    if(s[m] >= f[k]) {
+      k = m;
+      list_add(A, m);
+    }
+  }
+  return A;
+}

greedy_algorithms/activity_select/readme

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+Greedy solution to the activity selection problem from Cormen's Introduction to Algorithms.