Problem p01863 (C++)

Buggy submission (status: Runtime Error):
#include <bits/stdc++.h>

using namespace std;

const int INF = 1 << 30;

struct SuffixArray {
  vector<int> SA;
  string s;

  void Build_SA(const string &str) {
    s = str;
    SA.resize(s.size());
    iota(begin(SA), end(SA), 0);
    sort(begin(SA), end(SA), [&](const int &a, const int &b) {
      if (s[a] == s[b])
        return (a > b);
      return (s[a] < s[b]);
    });
    vector<int> classes(s.size()), c(s.size()), cnt(s.size());
    for (int i = 0; i < s.size(); i++) {
      c[i] = s[i];
    }
    for (int len = 1; len < s.size(); len <<= 1) {
      for (int i = 0; i < s.size(); i++) {
        if (i > 0 && c[SA[i - 1]] == c[SA[i]] && SA[i - 1] + len < s.size() &&
            c[SA[i - 1] + len / 2] == c[SA[i] + len / 2]) {
          classes[SA[i]] = classes[SA[i - 1]];
        } else {
          classes[SA[i]] = i;
        }
      }
      iota(begin(cnt), end(cnt), 0);
      copy(begin(SA), end(SA), begin(c));
      for (int i = 0; i < s.size(); i++) {
        int s1 = c[i] - len;
        if (s1 >= 0)
          SA[cnt[classes[s1]]++] = s1;
      }
      classes.swap(c);
    }
  }

  int operator[](int k) const { return (SA[k]); }

  int size() const { return (s.size()); }

  bool lt_substr(string &t, int si = 0, int ti = 0) {
    int sn = s.size(), tn = t.size();
    while (si < sn && ti < tn) {
      if (s[si] < t[ti])
        return (true);
      if (s[si] > t[ti])
        return (false);
      ++si, ++ti;
    }
    return (si >= sn && ti < tn);
  }

  int lower_bound(string &t) {
    int low = -1, high = SA.size();
    while (high - low > 1) {
      int mid = (low + high) >> 1;
      if (lt_substr(t, SA[mid]))
        low = mid;
      else
        high = mid;
    }
    return (high);
  }

  pair<int, int> lower_upper_bound(string &t) {
    int idx = lower_bound(t);
    int low = idx - 1, high = SA.size();
    t.back()++;
    while (high - low > 1) {
      int mid = (low + high) >> 1;
      if (lt_substr(t, SA[mid]))
        low = mid;
      else
        high = mid;
    }
    t.back()--;
    return (make_pair(idx, high));
  }
};

struct LongestCommonPrefixArray {
  vector<int> LCP;
  vector<int> rank;

  void Build_LCP(SuffixArray &SA) {
    string &s = SA.s;
    rank.resize(s.size());
    for (int i = 0; i < s.size(); i++) {
      rank[SA[i]] = i;
    }
    LCP.resize(s.size() - 1);
    for (int i = 0, h = 0; i < s.size(); i++) {
      if (rank[i] + 1 < s.size()) {
        for (int j = SA[rank[i] + 1];
             max(i, j) + h < s.length() && s[i + h] == s[j + h]; ++h)
          ;
        LCP[rank[i]] = h;
        if (h > 0)
          --h;
      }
    }
  }

  int operator[](int k) const {
    if (k < 0)
      return (0);
    return (LCP[k]);
  }

  int size() const { return (LCP.size() + 1); }
};

struct StaticSegmentTree {
  vector<int> seg;
  int sz;

  StaticSegmentTree(int n) {
    sz = 1;
    while (sz < n)
      sz <<= 1;
    seg.assign(2 * sz - 1, INF);
  }

  void set(int k, int x) { seg[k + sz - 1] = x; }

  void build() {
    for (int k = sz - 2; k >= 0; k--) {
      seg[k] = min(seg[2 * k + 1], seg[2 * k + 2]);
    };
  }

  int rmq(int a, int b, int k, int l, int r) {
    if (a >= r || b <= l)
      return (INF);
    if (a <= l && r <= b)
      return (seg[k]);
    return (min(rmq(a, b, 2 * k + 1, l, (l + r) >> 1),
                rmq(a, b, 2 * k + 2, (l + r) >> 1, r)));
  }

  int rmq(int a, int b) { return (rmq(min(a, b), max(a, b), 0, 0, sz)); }
};

int main() {
  string S;
  cin >> S;
  SuffixArray sa;
  sa.Build_SA(S);
  LongestCommonPrefixArray lcp;
  lcp.Build_LCP(sa);
  StaticSegmentTree tree(lcp.size());
  for (int i = 0; i < S.size(); i++) {
    tree.set(i, lcp[i]);
  }
  tree.build();

  int ret = INF;
  for (int A = 1; A < S.size(); A++) {
    int B = (int)S.size() - A * 3;
    if (B <= 0)
      break;
    if (B & 1)
      continue;
    B /= 2;
    if (tree.rmq(lcp.rank[0], lcp.rank[A + B]) >= A &&
        tree.rmq(lcp.rank[0], lcp.rank[A + B + A + B]) >= A &&
        tree.rmq(lcp.rank[A], lcp.rank[A + B + A]) >= B) {
      ret = min(ret, A + B);
    }
  }

  if (ret >= INF) {
    cout << "mitomerarenaiWA" << endl;
  } else {
    cout << "Love " << S.substr(0, ret) << "!" << endl;
  }
}

Fixed submission:
#include <bits/stdc++.h>

using namespace std;

const int INF = 1 << 30;

struct SuffixArray {
  vector<int> SA;
  string s;

  void Build_SA(const string &str) {
    s = str;
    SA.resize(s.size());
    iota(begin(SA), end(SA), 0);
    sort(begin(SA), end(SA), [&](const int &a, const int &b) {
      if (s[a] == s[b])
        return (a > b);
      return (s[a] < s[b]);
    });
    vector<int> classes(s.size()), c(s.size()), cnt(s.size());
    for (int i = 0; i < s.size(); i++) {
      c[i] = s[i];
    }
    for (int len = 1; len < s.size(); len <<= 1) {
      for (int i = 0; i < s.size(); i++) {
        if (i > 0 && c[SA[i - 1]] == c[SA[i]] && SA[i - 1] + len < s.size() &&
            c[SA[i - 1] + len / 2] == c[SA[i] + len / 2]) {
          classes[SA[i]] = classes[SA[i - 1]];
        } else {
          classes[SA[i]] = i;
        }
      }
      iota(begin(cnt), end(cnt), 0);
      copy(begin(SA), end(SA), begin(c));
      for (int i = 0; i < s.size(); i++) {
        int s1 = c[i] - len;
        if (s1 >= 0)
          SA[cnt[classes[s1]]++] = s1;
      }
      classes.swap(c);
    }
  }

  int operator[](int k) const { return (SA[k]); }

  int size() const { return (s.size()); }

  bool lt_substr(string &t, int si = 0, int ti = 0) {
    int sn = s.size(), tn = t.size();
    while (si < sn && ti < tn) {
      if (s[si] < t[ti])
        return (true);
      if (s[si] > t[ti])
        return (false);
      ++si, ++ti;
    }
    return (si >= sn && ti < tn);
  }

  int lower_bound(string &t) {
    int low = -1, high = SA.size();
    while (high - low > 1) {
      int mid = (low + high) >> 1;
      if (lt_substr(t, SA[mid]))
        low = mid;
      else
        high = mid;
    }
    return (high);
  }

  pair<int, int> lower_upper_bound(string &t) {
    int idx = lower_bound(t);
    int low = idx - 1, high = SA.size();
    t.back()++;
    while (high - low > 1) {
      int mid = (low + high) >> 1;
      if (lt_substr(t, SA[mid]))
        low = mid;
      else
        high = mid;
    }
    t.back()--;
    return (make_pair(idx, high));
  }
};

struct LongestCommonPrefixArray {
  vector<int> LCP;
  vector<int> rank;

  void Build_LCP(SuffixArray &SA) {
    string &s = SA.s;
    rank.resize(s.size());
    for (int i = 0; i < s.size(); i++) {
      rank[SA[i]] = i;
    }
    LCP.resize(s.size() - 1);
    for (int i = 0, h = 0; i < s.size(); i++) {
      if (rank[i] + 1 < s.size()) {
        for (int j = SA[rank[i] + 1];
             max(i, j) + h < s.length() && s[i + h] == s[j + h]; ++h)
          ;
        LCP[rank[i]] = h;
        if (h > 0)
          --h;
      }
    }
  }

  int operator[](int k) const {
    if (k < 0)
      return (0);
    return (LCP[k]);
  }

  int size() const { return (LCP.size() + 1); }
};

struct StaticSegmentTree {
  vector<int> seg;
  int sz;

  StaticSegmentTree(int n) {
    sz = 1;
    while (sz < n)
      sz <<= 1;
    seg.assign(2 * sz - 1, INF);
  }

  void set(int k, int x) { seg[k + sz - 1] = x; }

  void build() {
    for (int k = sz - 2; k >= 0; k--) {
      seg[k] = min(seg[2 * k + 1], seg[2 * k + 2]);
    };
  }

  int rmq(int a, int b, int k, int l, int r) {
    if (a >= r || b <= l)
      return (INF);
    if (a <= l && r <= b)
      return (seg[k]);
    return (min(rmq(a, b, 2 * k + 1, l, (l + r) >> 1),
                rmq(a, b, 2 * k + 2, (l + r) >> 1, r)));
  }

  int rmq(int a, int b) { return (rmq(min(a, b), max(a, b), 0, 0, sz)); }
};

int main() {
  string S;
  cin >> S;
  SuffixArray sa;
  sa.Build_SA(S);
  LongestCommonPrefixArray lcp;
  lcp.Build_LCP(sa);
  StaticSegmentTree tree(lcp.size());
  for (int i = 0; i < lcp.size() - 1; i++) {
    tree.set(i, lcp[i]);
  }
  tree.build();

  int ret = INF;
  for (int A = 1; A < S.size(); A++) {
    int B = (int)S.size() - A * 3;
    if (B <= 0)
      break;
    if (B & 1)
      continue;
    B /= 2;
    if (tree.rmq(lcp.rank[0], lcp.rank[A + B]) >= A &&
        tree.rmq(lcp.rank[0], lcp.rank[A + B + A + B]) >= A &&
        tree.rmq(lcp.rank[A], lcp.rank[A + B + A]) >= B) {
      ret = min(ret, A + B);
    }
  }

  if (ret >= INF) {
    cout << "mitomerarenaiWA" << endl;
  } else {
    cout << "Love " << S.substr(0, ret) << "!" << endl;
  }
}