Problem p03054 (C++)

Buggy submission (status: Runtime Error):
#include <bits/stdc++.h>
#define lsb(x) (x & (-x))
#define ll long long
#define ull unsigned long long

#if 0
const int MOD = ;

inline int lgput(int a, int b) {
    int ans = 1;
    while(b > 0) {
        if(b & 1) ans = (1LL * ans * a) % MOD;
        b >>= 1;
        a = (1LL * a * a) % MOD;
    }
    return ans;
}

inline void mod(int &x) {
    if(x >= MOD)
        x -= MOD;
}

inline void add(int &x, int y) {
    x += y;
    mod(x);
}

inline void sub(int &x, int y) {
    x += MOD - y;
    mod(x);
}

inline void mul(int &x, int y) {
    x = (1LL * x * y) % MOD;
}

inline int inv(int x) {
    return lgput(x, MOD - 2);
}
#endif

#if 0
int fact[], invfact[];

inline void prec(int n) {
    fact[0] = 1;
    for(int i = 1; i <= n; i++) {
        fact[i] = (1LL * fact[i - 1] * i) % MOD;
    }
    invfact[n] = lgput(fact[n], MOD - 2);
    for(int i = n - 1; i >= 0; i--) {
        invfact[i] = (1LL * invfact[i + 1] * (i + 1)) % MOD;
    }
}

inline int comb(int n, int k) {
    if(n < k) return 0;
    return (1LL * fact[n] * (1LL * invfact[k] * invfact[n - k] % MOD)) % MOD;
}
#endif

using namespace std;

const int MAXN = (int)2e5 + 5;

char s[MAXN], t[MAXN], str[2 * MAXN + 1];

pair<int, int> dpl[MAXN], dpc[MAXN];
int n;

inline void inter(int &l, int &r, int a, int b) {
  if (l > r) {
    cout << "NO";
    exit(0);
  }
  l = max(l, a);
  r = min(r, b);
}

inline void solve(pair<int, int> *dp, int h, char ch1, char ch2) {
  for (int i = 2 * n; i >= 1; i--) {
    int cur = 0;
    if (ch1 == str[i])
      cur--;
    if (ch2 == str[i])
      cur++;
    int l, r;
    if (i % 2 == 1) {
      l = 0, r = h + 1;
      inter(l, r, dp[i + 1].first, dp[i + 1].second);
      inter(l, r, dp[i + 1].first - cur, dp[i + 1].second - cur);
    } else {
      l = h + 1, r = 0;
      l = min(l, min(dp[i + 1].first, dp[i + 1].first - cur));
      r = max(r, max(dp[i + 1].second, dp[i + 1].second - cur));
    }
    inter(l, r, 1, h);
    dp[i] = {l, r};
  }
}

int main() {
#if 0
    ifstream cin("A.in");
    ofstream cout("A.out");
#endif
  int i, h, w, sl, sc;
  ios::sync_with_stdio(false);
  cin.tie(0), cout.tie(0);

  cin >> h >> w >> n;
  cin >> sl >> sc;
  cin >> s + 1 >> t + 1;

  for (i = 0; i < n; i++) {
    str[2 * i + 1] = s[i + 1];
    str[2 * i + 2] = t[i + 1];
  }

  dpl[2 * n + 1] = {1, h};
  dpc[2 * n + 1] = {1, w};

  solve(dpl, h, 'U', 'D');
  solve(dpc, w, 'L', 'R');

  if (dpl[1].first <= sl && dpl[1].second >= sl && dpc[1].first <= sc &&
      dpc[1].second >= sc) {
    cout << "YES";
    return 0;
  }
  cout << "NO";

  return 0;
}


Fixed submission:
#include <bits/stdc++.h>
#define lsb(x) (x & (-x))
#define ll long long
#define ull unsigned long long

#if 0
const int MOD = ;

inline int lgput(int a, int b) {
    int ans = 1;
    while(b > 0) {
        if(b & 1) ans = (1LL * ans * a) % MOD;
        b >>= 1;
        a = (1LL * a * a) % MOD;
    }
    return ans;
}

inline void mod(int &x) {
    if(x >= MOD)
        x -= MOD;
}

inline void add(int &x, int y) {
    x += y;
    mod(x);
}

inline void sub(int &x, int y) {
    x += MOD - y;
    mod(x);
}

inline void mul(int &x, int y) {
    x = (1LL * x * y) % MOD;
}

inline int inv(int x) {
    return lgput(x, MOD - 2);
}
#endif

#if 0
int fact[], invfact[];

inline void prec(int n) {
    fact[0] = 1;
    for(int i = 1; i <= n; i++) {
        fact[i] = (1LL * fact[i - 1] * i) % MOD;
    }
    invfact[n] = lgput(fact[n], MOD - 2);
    for(int i = n - 1; i >= 0; i--) {
        invfact[i] = (1LL * invfact[i + 1] * (i + 1)) % MOD;
    }
}

inline int comb(int n, int k) {
    if(n < k) return 0;
    return (1LL * fact[n] * (1LL * invfact[k] * invfact[n - k] % MOD)) % MOD;
}
#endif

using namespace std;

const int MAXN = (int)2e5 + 5;

char s[MAXN], t[MAXN], str[2 * MAXN + 1];

pair<int, int> dpl[2 * MAXN], dpc[2 * MAXN];
int n;

inline void inter(int &l, int &r, int a, int b) {
  if (l > r) {
    cout << "NO";
    exit(0);
  }
  l = max(l, a);
  r = min(r, b);
}

inline void solve(pair<int, int> *dp, int h, char ch1, char ch2) {
  for (int i = 2 * n; i >= 1; i--) {
    int cur = 0;
    if (ch1 == str[i])
      cur--;
    if (ch2 == str[i])
      cur++;
    int l, r;
    if (i % 2 == 1) {
      l = 0, r = h + 1;
      inter(l, r, dp[i + 1].first, dp[i + 1].second);
      inter(l, r, dp[i + 1].first - cur, dp[i + 1].second - cur);
    } else {
      l = h + 1, r = 0;
      l = min(l, min(dp[i + 1].first, dp[i + 1].first - cur));
      r = max(r, max(dp[i + 1].second, dp[i + 1].second - cur));
    }
    inter(l, r, 1, h);
    dp[i] = {l, r};
  }
}

int main() {
#if 0
    ifstream cin("A.in");
    ofstream cout("A.out");
#endif
  int i, h, w, sl, sc;
  ios::sync_with_stdio(false);
  cin.tie(0), cout.tie(0);

  cin >> h >> w >> n;
  cin >> sl >> sc;
  cin >> s + 1 >> t + 1;

  for (i = 0; i < n; i++) {
    str[2 * i + 1] = s[i + 1];
    str[2 * i + 2] = t[i + 1];
  }

  dpl[2 * n + 1] = {1, h};
  dpc[2 * n + 1] = {1, w};

  solve(dpl, h, 'U', 'D');
  solve(dpc, w, 'L', 'R');

  if (dpl[1].first <= sl && dpl[1].second >= sl && dpc[1].first <= sc &&
      dpc[1].second >= sc) {
    cout << "YES";
    return 0;
  }
  cout << "NO";

  return 0;
}