MLE and WA.

2023205/main.cpp

@@ -2,8 +2,9 @@
 // 并查集。并查集只关注双向连通性。
 
 struct Edge {
-    unsigned short end;
     int next;
+    unsigned short end;
+    bool used_in_dfs;
 };
 
 Edge edges[1050000];
@@ -19,13 +20,35 @@ int add_edge(int start, int terminal) {
 
 int dfs(int start) {
     if (nodes_visited[start] >= 1) {
-        nodes_visited[start] = 2;
+        // nodes_visited[start] = 2;
         return 0;
     }
     nodes_visited[start] = 1;
+    for (int j = head[start]; j != 0; j = edges[j].next) {
+        edges[j].used_in_dfs = dfs(edges[j].end);
+    }
+    return 1;
+}
+
+int dfs_with_dead_edge(int start, int dead_edge_start, int dead_edge_end) {
+    if (nodes_visited[start] >= 1) {
+        return 0;
+    }
+    nodes_visited[start] = 1;
+    if (start == dead_edge_start) {
+        for (int j = head[start]; j != 0; j = edges[j].next) {
+            if (edges[j].end == dead_edge_end) {
+                continue;
+            }
+            dfs(edges[j].end);
+        }
+        return 0;
+    }
+
     for (int j = head[start]; j != 0; j = edges[j].next) {
         dfs(edges[j].end);
     }
+
     return 0;
 }
 
@@ -41,10 +64,10 @@ int main() {
             add_edge(start, terminal);
         }
     }
-    
+
     dfs(0);
 
-    for (int i  = 0; i < N; i++) {
+    for (int i = 0; i < N; i++) {
         if (nodes_visited[i] < 1) {
             // Not connected!
             for (int j = 0; j <= M; j++) {
@@ -56,16 +79,46 @@ int main() {
 
     printf("1\n");
 
+    // for (int i = 0; i < M; i++) {
+    //     int start, end;
+    //     scanf("%d %d", &start, &end);
+    //     if (nodes_visited[end] == 2) {
+    //         printf("1\n");
+    //     }
+    //     else {
+    //         printf("0\n");
+    //     }
+    // }
+
     for (int i = 0; i < M; i++) {
         int start, end;
         scanf("%d %d", &start, &end);
-        if (nodes_visited[end] == 2) {
-            printf("1\n");
-        }
-        else {
-            printf("0\n");
+        for (int j = head[start]; j != 0; j = edges[j].next) {
+            if (edges[j].end == end) {
+                if (edges[j].used_in_dfs) {
+                    for (int k = 0; k < N; k++) {
+                        nodes_visited[k] = 0;
+                    }
+                    dfs_with_dead_edge(0, start, end);
+
+                    bool connected = true;
+                    for (int k = 0; k < N; k++) {
+                        if (nodes_visited[k] < 1) {
+                            printf("0\n");
+                            connected = false;
+                            break;
+                        }
+                    }
+                    if (connected) {
+                        printf("1\n");
+                    } 
+                }
+                else {
+                    printf("1\n");
+                }
+                break;
+            }
         }
     }
-
     return 0;
 }

2023205/testdat.txt

@@ -0,0 +1,4 @@
+4 2 2 1 2 2 2 3 0 1 0 0 1 0 2
+
+4 1 1 1 2 2 3 2 1 3 2 1 2 0 1
+