Problem p02671 (C++) — buggy submission, verdict: Runtime Error

#include <cstdio>
#include <cstring>
#include <iostream>
#include <vector>
using namespace std;
const int M = 15, N = 600005;
int n, m, Q;
char s[N];
int Pw[M];
struct Trie {
  struct Node {
    int ch[3];
    int val;
    int tag;
    Node() {
      ch[0] = ch[1] = ch[2] = 0;
      val = -1;
      tag = 0;
      return;
    }
  } trie[N * 3];
  int tot = 1;
  void insert(int x) {
    vector<int> v;
    int t = x;
    while (t)
      v.push_back(t % 3), t /= 3;
    while (v.size() < m)
      v.push_back(0);
    int u = 1;
    for (int c : v) {
      if (!trie[u].ch[c])
        trie[u].ch[c] = ++tot;
      u = trie[u].ch[c];
    }
    trie[u].val = x;
    return;
  }
  void push_down(int u) {
    if (!trie[u].tag)
      return;
    swap(trie[u].ch[1], trie[u].ch[2]);
    for (int i = 0; i < 3; i++)
      trie[trie[u].ch[i]].tag ^= 1;
    trie[u].tag = 0;
    return;
  }
  void reverse(int u) {
    trie[u].tag ^= 1;
    return;
  }
  void add(int u) {
    if (!u)
      return;
    push_down(u);
    int t = trie[u].ch[2];
    trie[u].ch[2] = trie[u].ch[1];
    trie[u].ch[1] = trie[u].ch[0];
    trie[u].ch[0] = t;
    add(trie[u].ch[0]);
    return;
  }
  void query(int u, int sum, int dep, vector<int> &res) {
    if (!u)
      return;
    push_down(u);
    if (trie[u].val != -1)
      res[trie[u].val] = sum;
    for (int i = 0; i < 3; i++)
      query(trie[u].ch[i], sum + i * Pw[dep], dep + 1, res);
    return;
  }
} T;
int main() {
  scanf("%d", &m);
  Pw[0] = 1;
  for (int i = 1; i <= m; i++)
    Pw[i] = Pw[i - 1] * 3;
  n = Pw[m];
  scanf("%s", s + 1);
  Q = strlen(s + 1);
  for (int i = 0; i < n; i++)
    T.insert(i);
  for (int i = 1; i <= Q; i++)
    if (s[i] == 'S')
      T.reverse(1);
    else if (s[i] == 'R')
      T.add(1);
  vector<int> res;
  res.resize(n);
  T.query(1, 0, 0, res);
  for (int u : res)
    printf("%d ", u);
  return 0;
}

Error: WA

Fixed submission:

#include <cstdio>
#include <cstring>
#include <iostream>
#include <vector>
using namespace std;
const int M = 15, N = 600005;
int n, m, Q;
char s[N];
int Pw[M];
struct Trie {
  struct Node {
    int ch[3];
    int val;
    int tag;
    Node() {
      ch[0] = ch[1] = ch[2] = 0;
      val = -1;
      tag = 0;
      return;
    }
  } trie[N];
  int tot = 1;
  void insert(int x) {
    vector<int> v;
    int t = x;
    while (t)
      v.push_back(t % 3), t /= 3;
    while (v.size() < m)
      v.push_back(0);
    int u = 1;
    for (int c : v) {
      if (!trie[u].ch[c])
        trie[u].ch[c] = ++tot;
      u = trie[u].ch[c];
    }
    trie[u].val = x;
    return;
  }
  void push_down(int u) {
    if (!trie[u].tag)
      return;
    swap(trie[u].ch[1], trie[u].ch[2]);
    for (int i = 0; i < 3; i++)
      trie[trie[u].ch[i]].tag ^= 1;
    trie[u].tag = 0;
    return;
  }
  void reverse(int u) {
    trie[u].tag ^= 1;
    return;
  }
  void add(int u) {
    if (!u)
      return;
    push_down(u);
    int t = trie[u].ch[2];
    trie[u].ch[2] = trie[u].ch[1];
    trie[u].ch[1] = trie[u].ch[0];
    trie[u].ch[0] = t;
    add(trie[u].ch[0]);
    return;
  }
  void query(int u, int sum, int dep, vector<int> &res) {
    if (!u)
      return;
    push_down(u);
    if (trie[u].val != -1)
      res[trie[u].val] = sum;
    for (int i = 0; i < 3; i++)
      query(trie[u].ch[i], sum + i * Pw[dep], dep + 1, res);
    return;
  }
} T;
int main() {
  scanf("%d", &m);
  Pw[0] = 1;
  for (int i = 1; i <= m; i++)
    Pw[i] = Pw[i - 1] * 3;
  n = Pw[m];
  scanf("%s", s + 1);
  Q = strlen(s + 1);
  for (int i = 0; i < n; i++)
    T.insert(i);
  for (int i = 1; i <= Q; i++)
    if (s[i] == 'S')
      T.reverse(1);
    else if (s[i] == 'R')
      T.add(1);
  vector<int> res;
  res.resize(n);
  T.query(1, 0, 0, res);
  for (int u : res)
    printf("%d ", u);
  return 0;
}