AoC 16 Part 2, works for all offsets

aoc16.cc

#include <vector>

int main() {
  //char cdat[] = "12345678";
  char cdat[] = "59791911701697178620772166487621926539855976237879300869872931303532122404711706813176657053802481833015214226705058704017099411284046473395211022546662450403964137283487707691563442026697656820695854453826690487611172860358286255850668069507687936410599520475680695180527327076479119764897119494161366645257480353063266653306023935874821274026377407051958316291995144593624792755553923648392169597897222058613725620920233283869036501950753970029182181770358827133737490530431859833065926816798051237510954742209939957376506364926219879150524606056996572743773912030397695613203835011524677640044237824961662635530619875905369208905866913334027160178";
  //char cdat[] = "03036732577212944063491565474664";
  int N = strlen(cdat)*10000;
  int *dat = new int[N];
  int *cc = new int[N+1];
  for (int j = 0; j < N; j+=strlen(cdat)) {
    for (int i = 0; i < strlen(cdat); i++) dat[j+i] = cdat[i] - '0';
  }
  cdat[7] = '\0';
  int off = atoi(cdat);

  std::vector<std::vector<int> > blks(N);

  printf("building\n");
  for (int i = 0; i < N; i++) {
    int off = i;
    blks[i].push_back(off);
    while (off < N) {
      off += (i+1);
      int t = std::min(N, off);
      blks[i].push_back(t);
    }
    blks[i].resize((blks[i].size()/2)*2);
    //printf("%d: %d\n", i, blks[i].size());
  }
  printf("done\n");

  for (int phase = 0; phase < 100; phase++) {
    printf("%d\n", phase);
    cc[0] = 0;
    for (int i = 0; i < N; i++) {
      cc[i+1] = cc[i] + dat[i];
    }
    for (int i = 0; i < N; i++) {
      int acc = 0;
      int pol = 1;
      //printf("%d\n", i);
      for (int j = 0; j < blks[i].size(); j += 2) {
        int t1 = blks[i][j];
        int t2 = blks[i][j+1];
        //printf("%d %d\n", t1, t2);
        acc += (cc[t2]-cc[t1]) * pol;
        pol *= -1;
      }
      // fix
      if (acc<0) acc *= -1;
      dat[i] = acc%10;
    }
  }
  //for (int i = 0; i < N; i++) printf("%d", dat[i]); printf("\n");
  for (int i = off; i < off+8; i++) printf("%d", dat[i]); printf("\n");
}