NHOI2015D 字符串

贪心 字符串查找

#include <cstdio>
#include <cstring>
using namespace std;
const int base = 52, MOD = 4999661, MAXN = 1e6 + 1;
char s[MAXN], t[MAXN];
int i, j, ans, lens, lent, hashs, hasht, tmp;
int main() {
  freopen("string.in", "r", stdin);
  freopen("string.out", "w", stdout);
  scanf("%s", s);
  scanf("%s", t);
  lens = strlen(s);
  lent = strlen(t);
  for (i = 0; i < lens; i++)
    s[i] -= (s[i] >= 'A' && s[i] <= 'Z') ? 'A' : ('a' - 26);
  for (i = 0; i < lent; i++)
    t[i] -= (t[i] >= 'A' && t[i] <= 'Z') ? 'A' : ('a' - 26);
  hashs = s[0];
  hasht = t[0];
  tmp = 1;
  for (i = 1; i < lens; i++) {
    ((hashs *= base) += s[i]) %= MOD;
    ((hasht *= base) += t[i]) %= MOD;
    (tmp *= base) %= MOD;
  }
  for (j = lens; j <= lent; )
    if (hashs == hasht) {
      ans++;
      if (j + lens <= lent) {
        hasht = 0;
        for (i = j; i < j + lens; i++)
          ((hasht *= base) += t[i]) %= MOD;
        j += lens;
      }
      else
        break;
    } else {
      hasht = ((hasht - t[j - lens] * tmp % MOD + MOD) % MOD * base + t[j]) % MOD;
      j++;
    }
  printf("%d\n", ans);
  return 0;
}