solution.c

#include <stdbool.h>

int captureForts(int* forts, int fortsSize) {
  for (int i = fortsSize - 1; i > 0; --i) {
    if (forts[i] == 0) continue;

    int maxCapture = 0;
    int possibleCapture = 0;
    bool prevEmpty = forts[i] == -1;

    while (--i > 0) {
      switch (forts[i]) {
        case -1:
          if (!prevEmpty) {
            prevEmpty = true;
            if (possibleCapture > maxCapture) maxCapture = possibleCapture;
          }
          possibleCapture = 0;
          break;

        case 0:
          ++possibleCapture;
          break;

        case 1:
          if (prevEmpty) {
            prevEmpty = false;
            if (possibleCapture > maxCapture) maxCapture = possibleCapture;
          }
          possibleCapture = 0;
      }
    }

    switch (forts[i]) {
      case -1:
        if (!prevEmpty && possibleCapture > maxCapture) {
          maxCapture = possibleCapture;
        }
        break;

      case 1:
        if (prevEmpty && possibleCapture > maxCapture) {
          maxCapture = possibleCapture;
        }
    }

    return maxCapture;
  }
  return 0;
}