Init

ACMOJ-2033.cpp

@@ -0,0 +1,53 @@
+#include <algorithm>
+#include <cassert>
+#include <cstdio>
+#include <cstring>
+using namespace std;
+typedef long long LL;
+const int maxn = 1e6 + 10;
+const __int128_t kBase = 114513;
+const __int128_t kMod = 180143985094819841ll;
+int n;
+char s[maxn];
+int f[maxn];
+__int128_t kPow[maxn], hsh[maxn];
+inline bool IsSame(int L1, int R1, int L2, int R2) {
+  if (R1 - L1 != R2 - L2) return false;
+  __int128_t hsh_s1 =
+      ((hsh[R1] - hsh[L1 - 1] * kPow[R1 - L1 + 1]) % kMod + kMod) % kMod;
+  __int128_t hsh_s2 =
+      ((hsh[R2] - hsh[L2 - 1] * kPow[R2 - L2 + 1]) % kMod + kMod) % kMod;
+  return hsh_s1 == hsh_s2;
+}
+int main() {
+#ifdef local
+  freopen("pro.in", "r", stdin);
+#endif
+  scanf("%d%s", &n, s + 1);
+  kPow[0] = 1;
+  for (int i = 1; i <= n; i++) {
+    kPow[i] = (kPow[i - 1] * kBase) % kMod;
+  }
+  for (int i = 1; i <= n; i++) {
+    hsh[i] = (hsh[i - 1] * kBase + s[i] - 'a' + 1) % kMod;
+  }
+  for (int i = n / 2; i > 0; i--) {
+    f[i] = f[i + 1] + 2;
+    while (f[i]) {
+      if ((i + f[i]) * 2 > n)
+        f[i]--;
+      else if (!IsSame(i + 1, i + f[i], n - i - f[i] + 1, n - i))
+        f[i]--;
+      else
+        break;
+    }
+  }
+  int ans = 0;
+  for (int i = 1; i * 2 <= n; i++)
+    if (IsSame(1, i, n - i + 1, n)) {
+      fprintf(stderr, "find i=%d\n", i);
+      ans = max(ans, i + f[i]);
+    }
+  printf("%d\n", ans);
+  return 0;
+}