'commit'

TangDou/AcWing/TwoWaySearch/190_Double_Bfs_YouHua_2.cpp

@@ -0,0 +1,85 @@
+#include <bits/stdc++.h>
+using namespace std;
+const int INF = 0x3f3f3f3f;
+const int N = 10;
+string A, B;                       //原始串
+string a[N], b[N];                 //规则
+queue<string> qa, qb;              //双端队列
+unordered_map<string, int> da, db; //此字符串，是几步转移过来的
+int n;
+int ans = INF;
+
+inline bool expandA() {
+    string u = qa.front();
+    qa.pop();
+    if (db.count(u)) {
+        ans = da[u] + db[u];
+        return true;
+    }
+    for (int i = 0; i < u.size(); i++) //枚举字符串的每一位
+        for (int j = 0; j < n; j++) {  //枚举规则
+            if (u.substr(i, a[j].size()) == a[j]) {
+                string ts = u.substr(0, i) + b[j] + u.substr(i + a[j].size());
+                if (!da.count(ts)) {
+                    qa.push(ts);
+                    da[ts] = da[u] + 1;
+                }
+            }
+        }
+    return false;
+}
+
+inline bool expandB() {
+    string u = qb.front();
+    qb.pop();
+    if (da.count(u)) {
+        ans = da[u] + db[u];
+        return true;
+    }
+    for (int i = 0; i < u.size(); i++)
+        for (int j = 0; j < n; j++) {
+            if (u.substr(i, b[j].size()) == b[j]) {
+                string ts = u.substr(0, i) + a[j] + u.substr(i + b[j].size());
+                if (!db.count(ts)) {
+                    qb.push(ts);
+                    db[ts] = db[u] + 1;
+                }
+            }
+        }
+    return false;
+}
+
+void bfs() {
+    //两个串分别入队列
+    qa.push(A), qb.push(B);
+    da[A] = 0, db[B] = 0;
+
+    //双向广搜套路
+    while (qa.size() && qb.size()) {
+        if (qa.size() < qb.size()) {
+            if (expandA()) return;
+            if (expandB()) return;
+        } else {
+            if (expandB()) return;
+            if (expandA()) return;
+        }
+    }
+}
+
+//可以AC掉本题,双向广搜+大小队列对比优化
+// 17ms
+int main() {
+    //加快读入
+    cin.tie(0), ios::sync_with_stdio(false);
+
+    cin >> A >> B;
+    while (cin >> a[n] >> b[n]) n++;
+
+    bfs();
+
+    if (ans > 10)
+        puts("NO ANSWER!");
+    else
+        printf("%d\n", ans);
+    return 0;
+}