#include <stdio.h> #include <stdlib.h> #include <string.h> #define N 30000 #define M_ 11111111 int min(int a, int b) { return a < b ? a : b; } void append(int **eh, int *eo, int i, int h) { int o = eo[i]++; if (o >= 2 && (o & o - 1) == 0) eh[i] = (int *) realloc(eh[i], o * 2 * sizeof *eh[i]); eh[i][o] = h; } int main() { static int *eh1[N + 1], eo1[N + 1], *eh2[N + 1], eo2[N + 1], ii[M_], jj[M_], hh[N], pp[M_], qq[M_], dd[M_], qu[M_ * 2]; int n, m, m_, h, i, j, o, head, cnt; scanf("%d%d", &n, &m); for (i = 0; i <= n; i++) { eh1[i] = (int *) malloc(2 * sizeof *eh1[i]); eh2[i] = (int *) malloc(2 * sizeof *eh2[i]); } for (h = 0; h < m; h++) { scanf("%d%d", &i, &j), j = min(j, n); ii[h] = i, jj[h] = j; append(eh1, eo1, i, h); append(eh2, eo2, j, h); } m_ = m; memset(hh, -1, n * sizeof *hh); memset(pp, -1, sizeof pp), memset(qq, -1, sizeof qq); for (j = 1; j < n; j++) { for (o = eo2[j]; o--; ) { h = eh2[j][o]; hh[ii[h]] = h; } for (o = eo2[j]; o--; ) { h = eh2[j][o]; if (hh[ii[h]] != -1) { for (i = ii[h] % j; i < n; i += j) if (hh[i] == -1) ii[m_] = i, jj[m_] = j, hh[i] = m_++; for (i = ii[h] % j; i < n; i += j) { if (i + j < n) qq[hh[i]] = hh[i + j], pp[hh[i + j]] = hh[i]; hh[i] = -1; } } } } for (h = 0; h < m_; h++) dd[h] = m_; head = m_, cnt = 0; dd[0] = 0, qu[head + cnt++] = 0; while (cnt) { int d, o; h = qu[cnt--, head++], i = ii[h], d = dd[h]; if (h == 1) { printf("%d\n", d); return 0; } for (o = eo1[i]; o--; ) { int h_ = eh1[i][o]; if (dd[h_] > d) dd[h_] = d, qu[cnt++, --head] = h_; } eo1[i] = 0; d++; if (pp[h] != -1 && dd[pp[h]] > d) dd[pp[h]] = d, qu[head + cnt++] = pp[h]; if (qq[h] != -1 && dd[qq[h]] > d) dd[qq[h]] = d, qu[head + cnt++] = qq[h]; } printf("-1\n"); return 0; }

skyscraper.c: In function 'append':
skyscraper.c:13:23: warning: suggest parentheses around '-' in operand of '&' [-Wparentheses]
   13 |  if (o >= 2 && (o & o - 1) == 0)
      |                     ~~^~~
skyscraper.c: In function 'main':
skyscraper.c:19:71: warning: variable 'jj' set but not used [-Wunused-but-set-variable]
   19 |  static int *eh1[N + 1], eo1[N + 1], *eh2[N + 1], eo2[N + 1], ii[M_], jj[M_], hh[N], pp[M_], qq[M_], dd[M_], qu[M_ * 2];
      |                                                                       ^~
skyscraper.c:22:2: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
   22 |  scanf("%d%d", &n, &m);
      |  ^~~~~~~~~~~~~~~~~~~~~
skyscraper.c:28:3: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
   28 |   scanf("%d%d", &i, &j), j = min(j, n);
      |   ^~~~~~~~~~~~~~~~~~~~~