20240418

ACMOJ-2133.cpp

@@ -0,0 +1,61 @@
+#include <algorithm>
+#include <cstdio>
+#include <cstring>
+using namespace std;
+typedef long long LL;
+const int kMod = 19930726;
+const int kMaxN = 1e6 + 10;
+int n;
+LL K;
+char s[kMaxN];
+int d1[kMaxN];
+LL cnt[kMaxN];
+LL qpow(int a, int b) {
+  LL res = 1;
+  while (b > 0) {
+    if (b & 1) res = (res * a) % kMod;
+    b >>= 1;
+    a = (a * (LL)a) % kMod;
+  }
+  return res;
+}
+int main() {
+#ifdef local
+  freopen("pro.in", "r", stdin);
+#endif
+  scanf("%d%lld", &n, &K);
+  scanf("%s", s);
+  for (int i = 0, l = 0, r = -1; i < n; i++) {
+    int k = (i > r) ? 1 : min(d1[l + r - i], r - i + 1);
+    while (0 <= i - k && i + k < n && s[i - k] == s[i + k]) { k++; }
+    d1[i] = k--;
+    if (i + k > r) {
+      l = i - k;
+      r = i + k;
+    }
+  }
+  LL tot = 0;
+  for (int i = 0; i < n; i++) {
+    tot += d1[i];
+    cnt[d1[i]]++;
+  }
+  if (tot < K) {
+    printf("-1\n");
+    return 0;
+  }
+  for(int i=n-1;i>=1;i--) cnt[i]+=cnt[i+1];
+  LL lft = K, res = 1;
+  for (int i = n; i >= 1; i--) {
+    if (cnt[i] > 0) {
+      if (cnt[i] < lft) {
+        res = (res * qpow(2 * i - 1, cnt[i])) % kMod;
+        lft -= cnt[i];
+      } else {
+        res = (res * qpow(2 * i - 1, lft)) % kMod;
+        break;
+      }
+    }
+  }
+  printf("%lld\n", res);
+  return 0;
+}