Problem p00247 (C++)

Buggy submission (status: Time Limit Exceeded):
#include <algorithm>
#include <complex>
#include <iostream>
#include <map>
#include <math.h>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <stdio.h>
#include <string.h>
#include <string>
#include <utility>
#include <vector>
using namespace std;
const int INF = 1 << 29;
const double EPS = 1e-8;
typedef vector<int> vec;
typedef vector<vec> mat;
typedef pair<int, int> P;
struct edge {
  int to, cost;
};

const int dx[] = {0, 0, 1, -1};
const int dy[] = {1, -1, 0, 0};

char field[12][12];
int ifield[12][12];
int W, H;

struct State {
  int d, y, x;
  vec ice;
};

string state2str(State &s) {
  string ret = "";
  ret.push_back(s.d + '0');
  ret.push_back(s.y + '0');
  ret.push_back(s.x + '0');
  for (int i = 0; i < s.ice.size(); i++) {
    ret.push_back(s.ice[i] + '0');
  }
  return ret;
}

int lump_ice_num;
int ice_num[12 * 12];
int dfs(int y, int x) {
  int ret = 1;
  ifield[y][x] = lump_ice_num;
  field[y][x] = '.';
  for (int i = 0; i < 4; i++) {
    int ny = y + dy[i], nx = x + dx[i];
    if (ny < 0 || H <= ny || nx < 0 || W <= nx)
      continue;
    if (field[ny][nx] == 'X') {
      ret += dfs(ny, nx);
    }
  }
  return ret;
}

bool visited[12][12];
int visited_ice[12 * 12];
int ans;
int sy, sx, gy, gx;
void dfs2(int y, int x, int py, int px, int d) {
  // printf("%d %d\n",y,x);
  if (d >= ans)
    return;
  if (y == gy && x == gx) {
    ans = min(d, ans);
    return;
  }
  for (int i = 0; i < 4; i++) {
    int ny = y + dy[i], nx = x + dx[i];
    if (ny < 0 || H <= ny || nx < 0 || W <= nx)
      continue;
    if (ny == py && nx == px)
      continue;
    if (visited[ny][nx])
      return;
  }
  visited[y][x] = true;
  for (int i = 0; i < 4; i++) {
    int ny = y + dy[i], nx = x + dx[i];
    if (ny < 0 || H <= ny || nx < 0 || W <= nx)
      continue;
    // printf("y=%d x=%d ny=%d nx=%d\n", y, x, ny, nx);
    if (visited[ny][nx])
      continue;
    if (ifield[ny][nx] == -2)
      continue;
    if (ifield[ny][nx] >= 0) {
      int ice_i = ifield[ny][nx];
      if (ice_num[ice_i] / 2 < visited_ice[ice_i] + 1)
        continue;
      visited_ice[ice_i]++;
      dfs2(ny, nx, y, x, d + 1);
      visited_ice[ice_i]--;
    } else {
      dfs2(ny, nx, y, x, d + 1);
    }
  }
  visited[y][x] = false;
}

int main() {
  while (cin >> W >> H, W) {
    for (int i = 0; i < H; i++) {
      for (int j = 0; j < W; j++) {
        cin >> field[i][j];
        if (field[i][j] == '.') {
          ifield[i][j] = -1;
        } else if (field[i][j] == '#') {
          ifield[i][j] = -2;
        } else if (field[i][j] == 'S') {
          ifield[i][j] = -1;
          sy = i;
          sx = j;
        } else if (field[i][j] == 'G') {
          ifield[i][j] = -1;
          gy = i;
          gx = j;
        }
      }
    }

    lump_ice_num = 0;
    for (int i = 0; i < H; i++) {
      for (int j = 0; j < W; j++) {
        if (field[i][j] == 'X') {
          ice_num[lump_ice_num] = dfs(i, j);
          lump_ice_num++;
        }
      }
    }

    ans = INF;
    memset(visited, 0, sizeof(visited));
    memset(visited_ice, 0, sizeof(visited_ice));
    dfs2(sy, sx, -1, -1, 0);
    cout << ans << endl;
  }

  return 0;
}

Fixed submission:
#include <algorithm>
#include <complex>
#include <iostream>
#include <map>
#include <math.h>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <stdio.h>
#include <string.h>
#include <string>
#include <utility>
#include <vector>
using namespace std;
const int INF = 1 << 29;
const double EPS = 1e-8;
typedef vector<int> vec;
typedef vector<vec> mat;
typedef pair<int, int> P;
struct edge {
  int to, cost;
};

const int dx[] = {0, 0, 1, -1};
const int dy[] = {1, -1, 0, 0};

char field[12][12];
int ifield[12][12];
int W, H;

struct State {
  int d, y, x;
  vec ice;
};

string state2str(State &s) {
  string ret = "";
  ret.push_back(s.d + '0');
  ret.push_back(s.y + '0');
  ret.push_back(s.x + '0');
  for (int i = 0; i < s.ice.size(); i++) {
    ret.push_back(s.ice[i] + '0');
  }
  return ret;
}

int lump_ice_num;
int ice_num[12 * 12];
int dfs(int y, int x) {
  int ret = 1;
  ifield[y][x] = lump_ice_num;
  field[y][x] = '.';
  for (int i = 0; i < 4; i++) {
    int ny = y + dy[i], nx = x + dx[i];
    if (ny < 0 || H <= ny || nx < 0 || W <= nx)
      continue;
    if (field[ny][nx] == 'X') {
      ret += dfs(ny, nx);
    }
  }
  return ret;
}

bool visited[12][12];
int visited_ice[12 * 12];
int ans;
int sy, sx, gy, gx;
void dfs2(int y, int x, int py, int px, int d) {
  // printf("%d %d\n",y,x);
  if (d >= ans)
    return;
  if (y == gy && x == gx) {
    ans = min(d, ans);
    return;
  }
  if (d + abs(gy - y) + abs(gx - x) >= ans)
    return;
  for (int i = 0; i < 4; i++) {
    int ny = y + dy[i], nx = x + dx[i];
    if (ny < 0 || H <= ny || nx < 0 || W <= nx)
      continue;
    if (ny == py && nx == px)
      continue;
    if (visited[ny][nx])
      return;
  }
  visited[y][x] = true;
  for (int i = 0; i < 4; i++) {
    int ny = y + dy[i], nx = x + dx[i];
    if (ny < 0 || H <= ny || nx < 0 || W <= nx)
      continue;
    // printf("y=%d x=%d ny=%d nx=%d\n", y, x, ny, nx);
    if (visited[ny][nx])
      continue;
    if (ifield[ny][nx] == -2)
      continue;
    if (ifield[ny][nx] >= 0) {
      int ice_i = ifield[ny][nx];
      if (ice_num[ice_i] / 2 < visited_ice[ice_i] + 1)
        continue;
      visited_ice[ice_i]++;
      dfs2(ny, nx, y, x, d + 1);
      visited_ice[ice_i]--;
    } else {
      dfs2(ny, nx, y, x, d + 1);
    }
  }
  visited[y][x] = false;
}

int main() {
  while (cin >> W >> H, W) {
    for (int i = 0; i < H; i++) {
      for (int j = 0; j < W; j++) {
        cin >> field[i][j];
        if (field[i][j] == '.') {
          ifield[i][j] = -1;
        } else if (field[i][j] == '#') {
          ifield[i][j] = -2;
        } else if (field[i][j] == 'S') {
          ifield[i][j] = -1;
          sy = i;
          sx = j;
        } else if (field[i][j] == 'G') {
          ifield[i][j] = -1;
          gy = i;
          gx = j;
        }
      }
    }

    lump_ice_num = 0;
    for (int i = 0; i < H; i++) {
      for (int j = 0; j < W; j++) {
        if (field[i][j] == 'X') {
          ice_num[lump_ice_num] = dfs(i, j);
          lump_ice_num++;
        }
      }
    }

    ans = INF;
    memset(visited, 0, sizeof(visited));
    memset(visited_ice, 0, sizeof(visited_ice));
    dfs2(sy, sx, -1, -1, 0);
    cout << ans << endl;
  }

  return 0;
}