Problem p00527 (C++)

Buggy submission (status: Runtime Error):
#include <algorithm>
#include <cmath>
#include <cstdio>
#include <functional>
#include <iomanip>
#include <iostream>
#include <list>
#include <map>
#include <queue>
#include <random>
#include <set>
#include <string>
#include <unordered_map>
#include <vector>
using namespace std;
//---------------------------------------------------
// ライブラリゾーン！！！！
#define int long long
#define str string
#define rep(i, j) for (int i = 0; i < (int)(j); i++)
typedef long long ll;
typedef long double ld;
const ll inf = 4523372036854775807;
const ll Mod = 1000000007;
short gh[2][4] = {{0, 0, -1, 1}, {-1, 1, 0, 0}};
struct P {
  ll pos, cost;
};
bool operator<(P a, P b) { return a.cost < b.cost; }
bool operator>(P a, P b) { return a.cost > b.cost; }
struct B { // 隣接リスト表現
  ll to, cost;
};
struct S { // 辺の情報を入れる変数
  int from, to, cost;
};
struct H {
  int x, y;
};
bool operator<(H a, H b) {
  if (a.x != b.x)
    return a.x < b.x;
  return a.y < b.y;
}
ll gcm(ll i, ll j) { // 最大公約数
  if (i > j)
    swap(i, j);
  if (i == 0)
    return j;
  return gcm(j % i, i);
}
ld rad(ld a, ld b, ld c, ld d) {
  return sqrt(pow(a - c, 2) + pow(b - d, 2));
} // rad＝座標上の2点間の距離
int ari(int a, int b, int c) { return (a + b) * c / 2; } // 等差数列の和
bool suf(ld a, ld b, ld c, ld d) {
  if (b <= c || d <= a)
    return 0;
  return 1;
} //[a,b),[c,d)
ll mod_pow(ll x, ll n, ll p) {
  ll res = 1;
  while (n > 0) {
    if (n & 1)
      res = res * x % p;
    x = x * x % p;
    n >>= 1;
  }
  return res;
}
//---------------------------------------------------
//+++++++++++++++++++++++++++++++++++++++++++++++++++
int n, m, ans;
string s1, s2;
int dp[2000][2000][2];
int solve(int x, int y, int z) {
  if (x == n && y == m) {
    if (z == 0)
      return -inf;
    return 0;
  }
  if (dp[x][y][z] > 0) {
    return dp[x][y][z];
  }
  int sum = 0;
  if (x < n) {
    if (s1[x] == 'O' && z == 1) {
      sum = max(sum, solve(x + 1, y, 0) + 1);
    }
    if (s1[x] == 'I' && z == 0) {
      sum = max(sum, solve(x + 1, y, 1) + 1);
    }
  }
  if (y < m) {
    if (s2[y] == 'O' && z == 1) {
      sum = max(sum, solve(x, y + 1, 0) + 1);
    }
    if (s2[y] == 'I' && z == 0) {
      sum = max(sum, solve(x, y + 1, 1) + 1);
    }
  }
  if (z == 0 && sum == 0) {
    sum = -inf;
  }
  ans = max(ans, sum);
  return dp[x][y][z] = sum;
}
signed main() {
  cin >> n >> m;
  cin >> s1 >> s2;
  for (int i = 0; i <= n; i++) {
    for (int j = 0; j <= m; j++) {
      solve(i, j, 0);
    }
  }
  cout << ans << endl;
  getchar();
  getchar();
}


Fixed submission:
#include <algorithm>
#include <cmath>
#include <cstdio>
#include <functional>
#include <iomanip>
#include <iostream>
#include <list>
#include <map>
#include <queue>
#include <random>
#include <set>
#include <string>
#include <unordered_map>
#include <vector>
using namespace std;
//---------------------------------------------------
// ライブラリゾーン！！！！
#define int long long
#define str string
#define rep(i, j) for (int i = 0; i < (int)(j); i++)
typedef long long ll;
typedef long double ld;
const ll inf = 4523372036854775807;
const ll Mod = 1000000007;
short gh[2][4] = {{0, 0, -1, 1}, {-1, 1, 0, 0}};
struct P {
  ll pos, cost;
};
bool operator<(P a, P b) { return a.cost < b.cost; }
bool operator>(P a, P b) { return a.cost > b.cost; }
struct B { // 隣接リスト表現
  ll to, cost;
};
struct S { // 辺の情報を入れる変数
  int from, to, cost;
};
struct H {
  int x, y;
};
bool operator<(H a, H b) {
  if (a.x != b.x)
    return a.x < b.x;
  return a.y < b.y;
}
ll gcm(ll i, ll j) { // 最大公約数
  if (i > j)
    swap(i, j);
  if (i == 0)
    return j;
  return gcm(j % i, i);
}
ld rad(ld a, ld b, ld c, ld d) {
  return sqrt(pow(a - c, 2) + pow(b - d, 2));
} // rad＝座標上の2点間の距離
int ari(int a, int b, int c) { return (a + b) * c / 2; } // 等差数列の和
bool suf(ld a, ld b, ld c, ld d) {
  if (b <= c || d <= a)
    return 0;
  return 1;
} //[a,b),[c,d)
ll mod_pow(ll x, ll n, ll p) {
  ll res = 1;
  while (n > 0) {
    if (n & 1)
      res = res * x % p;
    x = x * x % p;
    n >>= 1;
  }
  return res;
}
//---------------------------------------------------
//+++++++++++++++++++++++++++++++++++++++++++++++++++
int n, m, ans;
string s1, s2;
int dp[2001][2001][2];
int solve(int x, int y, int z) {
  if (x == n && y == m) {
    if (z == 0)
      return -inf;
    return 0;
  }
  if (dp[x][y][z] > 0) {
    return dp[x][y][z];
  }
  int sum = 0;
  if (x < n) {
    if (s1[x] == 'O' && z == 1) {
      sum = max(sum, solve(x + 1, y, 0) + 1);
    }
    if (s1[x] == 'I' && z == 0) {
      sum = max(sum, solve(x + 1, y, 1) + 1);
    }
  }
  if (y < m) {
    if (s2[y] == 'O' && z == 1) {
      sum = max(sum, solve(x, y + 1, 0) + 1);
    }
    if (s2[y] == 'I' && z == 0) {
      sum = max(sum, solve(x, y + 1, 1) + 1);
    }
  }
  if (z == 0 && sum == 0) {
    sum = -inf;
  }
  ans = max(ans, sum);
  return dp[x][y][z] = sum;
}
signed main() {
  cin >> n >> m;
  cin >> s1 >> s2;
  for (int i = 0; i <= n; i++) {
    for (int j = 0; j <= m; j++) {
      solve(i, j, 0);
    }
  }
  cout << ans << endl;
  getchar();
  getchar();
}