fix: new faster heuristic used in solution

ra-preguicosa/src/ac.cpp

@@ -1,7 +1,7 @@
 #include <bits/stdc++.h>
 
 #define endl '\n'
-#define INF 0x3f
+#define INF 0x3f3f3f3f
 
 using namespace std;
 
@@ -11,7 +11,6 @@ const int MAXN = 1e3 + 10;
 
 int C, L, W;
 int Cr, Lr, Cs, Ls;
-int alagado[MAXN][MAXN];
 const int COSTS[5][5] = {
    {7, 6, 5, 6, 7},
    {6, 3, 2, 3, 6},
@@ -19,67 +18,47 @@ const int COSTS[5][5] = {
    {6, 3, 2, 3, 6},
    {7, 6, 5, 6, 7},
 };
-int vis[MAXN][MAXN];
+bitset<MAXN> alagado[MAXN];
 int g[MAXN][MAXN];
 
 bool valid(int c, int l) {
    return c > 0 && c <= C && l > 0 && l <= L && alagado[c][l] == 0; 
 }
 
-int h(int c, int l)
-{
-   return sqrt(abs(Cs - c)*abs(Cs - c) + abs(Ls - l)*abs(Ls - l));
-}
+int h(int c, int l) {
+   int dx = abs(Cs - c);
+   int dy = abs(Ls - l);
 
-bool reachable()
-{
-   queue<pii> q;
-   memset(vis, 0, sizeof(vis));
+   int diag = min(dx, dy);
+   int straight = max(dx, dy) - diag;
 
-   q.push({Cr, Lr});
-   vis[Cr][Lr] = 1;
-
-   while (!q.empty())
-   {
-      auto [c, l] = q.front();
-      q.pop();
-
-      if (c == Cs && l == Ls) return true;
-
-      for (int i = -2; i <= 2; i++){
-         for (int j = -2; j <= 2; j++){
-            int nc = c + i, nl = l + j;
-            if (!valid(nc, nl) || vis[nc][nl]) continue;
-            vis[nc][nl] = 1;
-            q.push({nc, nl});
-         }
-      }
-   }
-
-   return false;
+   return diag * 3 + straight * 2;
 }
 
 void solve()
 {
-   if (!reachable())
-   {
-      cout << "impossible" << endl;
-      return;
+   for (int i = 1; i <= C; i++){
+      for (int j = 1; j <= L; j++){
+         g[i][j] = INF;
+      }
    }
 
-   memset(vis, 0, sizeof(vis));
-   memset(g, INF, sizeof(g));
-   priority_queue<pair<int, pii>> pq;
+    priority_queue<
+      pair<int, pii>,
+      vector<pair<int, pii>>,
+      greater<>
+    > pq;
+
    g[Cr][Lr] = 0;
-   pq.push({-h(Cr, Lr), {Cr, Lr}});
+   pq.push({h(Cr, Lr), {Cr, Lr}});
+
    while (!pq.empty()){
       auto [curCost, curCoords] = pq.top();
       pq.pop();
 
       auto [c, l] = curCoords;
 
-      if (vis[c][l]) continue;
-      vis[c][l] = 1;
+      if (curCost != g[c][l] + h(c,l)) continue;
 
       if (c == Cs && l == Ls){
          cout << g[c][l] << endl;
@@ -91,17 +70,18 @@ void solve()
             int nc = c + i, nl = l + j;
             if (!valid(nc, nl)) continue;
 
-            int cost = COSTS[i + 2][j + 2];
+            int cost = COSTS[i+2][j+2];
             int newG = g[c][l] + cost;
+
             if (newG < g[nc][nl]){
                g[nc][nl] = newG;
-               int f = g[nc][nl] + h(nc, nl);
-               // insere custo negativo pois por padrao a priority queue é uma max heap
-               pq.push({-f, {nc, nl}});
+               pq.push({newG + h(nc, nl), {nc, nl}});
             }
          }
       }
    }
+
+    cout << "impossible" << endl;
 }
 
 int main()
@@ -110,11 +90,13 @@ int main()
    cin.tie(nullptr);
 
    while (cin >> C >> L, C && L){
-      cin >> Cr >> Lr;
-      cin >> Cs >> Ls;
+      cin >> Cr >> Lr >> Cs >> Ls;
+      for (int i = 1; i <= C; i++){
+         for (int j = 1; j <= L; j++){
+               alagado[i][j]=0;
+         }
+      }
       cin >> W;
-      memset(alagado, 0, sizeof(alagado));
-      memset(vis, 0, sizeof(vis));
       for (int i = 0; i < W; i++){
          int C1, C2, L1, L2;
          cin >> C1 >> L1 >> C2 >> L2;