Problem p02589 (C++) — buggy submission, verdict: Time Limit Exceeded

#include <bits/stdc++.h>
#define LL long long
#define RG register

using namespace std;
template <class T> T gi() {
  T x = 0;
  bool f = 0;
  char c = getchar();
  while (c != '-' && (c < '0' || c > '9'))
    c = getchar();
  if (c == '-')
    f = 1, c = getchar();
  while (c >= '0' && c <= '9')
    x = x * 10 + c - '0', c = getchar();
  return f ? -x : x;
}
const int N = 2e6 + 10, Mod = 1e9 + 7;
int ch[N][26], cnt[N][26], tot, tim;
LL ans;
string s[N];
bool flg[26];
void insert(int k, int x) {
  if (k == -1)
    return;
  if (!ch[x][s[tim][k] - 'a'])
    ch[x][s[tim][k] - 'a'] = ++tot;
  insert(k - 1, ch[x][s[tim][k] - 'a']);
  flg[s[tim][k] - 'a'] = 1;
  for (int j = 0; j < 26; j++)
    if (flg[j])
      cnt[x][j]++;
}
int main() {
  int n = gi<int>();
  for (int i = 1; i <= n; i++) {
    cin >> s[i];
    tim = i;
    for (int j = 0; j < 26; j++)
      flg[j] = 0;
    insert(s[i].length() - 1, 0);
  }
  for (int i = 1; i <= n; i++) {
    int now = 0, len = s[i].length();
    for (int j = len - 1; j; j--)
      now = ch[now][s[i][j] - 'a'];
    ans += cnt[now][s[i][0] - 'a'];
  }
  printf("%lld\\n", ans - n);
  return 0;
}


Error: TLE

Fixed submission:

#define FASTER
#ifdef FASTER
#pragma GCC diagnostic error "-std=c++11"
#pragma GCC optimize(2)
#pragma GCC optimize(3)
#pragma GCC optimize("Ofast")
#pragma GCC optimize("inline")
#pragma GCC optimize("-fgcse")
#pragma GCC optimize("-fgcse-lm")
#pragma GCC optimize("-fipa-sra")
#pragma GCC optimize("-ftree-pre")
#pragma GCC optimize("-ftree-vrp")
#pragma GCC optimize("-fpeephole2")
#pragma GCC optimize("-ffast-math")
#pragma GCC optimize("-fsched-spec")
#pragma GCC optimize("unroll-loops")
#pragma GCC optimize("-falign-jumps")
#pragma GCC optimize("-falign-loops")
#pragma GCC optimize("-falign-labels")
#pragma GCC optimize("-fdevirtualize")
#pragma GCC optimize("-fcaller-saves")
#pragma GCC optimize("-fcrossjumping")
#pragma GCC optimize("-fthread-jumps")
#pragma GCC optimize("-funroll-loops")
#pragma GCC optimize("-fwhole-program")
#pragma GCC optimize("-freorder-blocks")
#pragma GCC optimize("-fschedule-insns")
#pragma GCC optimize("inline-functions")
#pragma GCC optimize("-ftree-tail-merge")
#pragma GCC optimize("-fschedule-insns2")
#pragma GCC optimize("-fstrict-aliasing")
#pragma GCC optimize("-fstrict-overflow")
#pragma GCC optimize("-falign-functions")
#pragma GCC optimize("-fcse-skip-blocks")
#pragma GCC optimize("-fcse-follow-jumps")
#pragma GCC optimize("-fsched-interblock")
#pragma GCC optimize("-fpartial-inlining")
#pragma GCC optimize("no-stack-protector")
#pragma GCC optimize("-freorder-functions")
#pragma GCC optimize("-findirect-inlining")
#pragma GCC optimize("-fhoist-adjacent-loads")
#pragma GCC optimize("-frerun-cse-after-loop")
#pragma GCC optimize("inline-small-functions")
#pragma GCC optimize("-finline-small-functions")
#pragma GCC optimize("-ftree-switch-conversion")
#pragma GCC optimize("-foptimize-sibling-calls")
#pragma GCC optimize("-fexpensive-optimizations")
#pragma GCC optimize("-funsafe-loop-optimizations")
#pragma GCC optimize("inline-functions-called-once")
#pragma GCC optimize("-fdelete-null-pointer-checks")
#endif
#include <bits/stdc++.h>
#define LL long long
#define RG register

using namespace std;
template <class T> T gi() {
  T x = 0;
  bool f = 0;
  char c = getchar();
  while (c != '-' && (c < '0' || c > '9'))
    c = getchar();
  if (c == '-')
    f = 1, c = getchar();
  while (c >= '0' && c <= '9')
    x = x * 10 + c - '0', c = getchar();
  return f ? -x : x;
}
const int N = 1e6 + 10, Mod = 1e9 + 7;
int ch[N][26], cnt[N][26], tot;
LL ans;
char str[N];
bool flg[26];
void insert(int k, int x) {
  if (k == -1)
    return;
  if (!ch[x][str[k] - 'a'])
    ch[x][str[k] - 'a'] = ++tot;
  insert(k - 1, ch[x][str[k] - 'a']);
  flg[str[k] - 'a'] = 1;
  for (int j = 0; j < 26; j++)
    if (flg[j])
      cnt[x][j]++;
}
string s[N];
int main() {
  //	freopen("in.in", "r", stdin);
  // freopen(".out", "w", stdout);
  int n = gi<int>();
  for (int i = 1; i <= n; i++) {
    scanf("%s", str);
    for (int j = 0; j < 26; j++)
      flg[j] = 0;
    for (int j = 0, len = strlen(str); j < len; j++)
      s[i] = s[i] + str[j];
    insert(strlen(str) - 1, 0);
  }
  for (int i = 1; i <= n; i++) {
    int now = 0, len = s[i].length();
    for (int j = len - 1; j; j--)
      now = ch[now][s[i][j] - 'a'];
    ans += cnt[now][s[i][0] - 'a'];
  }
  printf("%lld\\n", ans - n);
  return 0;
}