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  1. #include <bits/stdc++.h>
  2. using namespace std;
  3. #define itachi ios::sync_with_stdio(0); cin.tie(0);
  4.  
  5. struct Node {
  6.     int nxt[26];
  7.     int word;
  8.     vector<int> pal; 
  9.     Node() {
  10.         memset(nxt, -1, sizeof(nxt));
  11.         word = -1;
  12.     }
  13. };
  14.  
  15. const uint64_t base = 1315423911ull;  // big base
  16. const uint64_t mod1 = 1000000007ull;
  17. const uint64_t p = 911382323ull;      // random odd base
  18.  
  19. vector<uint64_t> pw;  // powers of base
  20.  
  21. struct HString {
  22.     string s;
  23.     int n;
  24.     vector<uint64_t> Hf, Hr;
  25.  
  26.     void build(const string &t) {
  27.         s = t;
  28.         n = s.size();
  29.         Hf.assign(n+1, 0);
  30.         Hr.assign(n+1, 0);
  31.  
  32.         for (int i = 0; i < n; ++i) {
  33.             Hf[i+1] = Hf[i] * p + (s[i] + 1);
  34.             Hr[i+1] = Hr[i] * p + (s[n-1-i] + 1);
  35.         }
  36.     }
  37.  
  38.     // hash forward of s[l..r]
  39.     uint64_t getF(int l, int r) const {
  40.         return Hf[r+1] - Hf[l] * pw[r-l+1];
  41.     }
  42.  
  43.     // hash backward of s[l..r]
  44.     uint64_t getR(int l, int r) const {
  45.         // map s[l..r] to reversed index
  46.         int rl = n-1-r;  
  47.         int rr = n-1-l;
  48.         return Hr[rr+1] - Hr[rl] * pw[rr-rl+1];
  49.     }
  50.  
  51.     inline bool isPal(int l, int r) const {
  52.         return getF(l, r) == getR(l, r);
  53.     }
  54. };
  55.  
  56.  
  57. int main(){
  58.     itachi;
  59.     int n;
  60.     cin >> n;
  61.  
  62.     vector<string> a(n);
  63.     long long total = 0;
  64.     for(int i = 0; i < n; ++i){
  65.         cin >> a[i];
  66.         total += a[i].size();
  67.     }
  68.  
  69.     // Precompute powers
  70.     pw.resize(total + 5);
  71.     pw[0] = 1;
  72.     for (int i = 1; i <= total; ++i)
  73.         pw[i] = pw[i-1] * p;
  74.  
  75.     // Build hash objects
  76.     vector<HString> H(n);
  77.     for (int i = 0; i < n; ++i)
  78.         H[i].build(a[i]);
  79.  
  80.     vector<Node> trie;
  81.     trie.reserve(total + 5);
  82.     trie.emplace_back();  // root = 0
  83.  
  84.     // Insert reversed words
  85.     for (int idx = 0; idx < n; ++idx) {
  86.         const string &w = a[idx];
  87.         int L = w.size();
  88.         int node = 0;
  89.  
  90.         for (int i = L - 1; i >= 0; --i) {
  91.  
  92.             if (H[idx].isPal(0, i))
  93.                 trie[node].pal.push_back(idx);
  94.  
  95.             int c = w[i] - 'a';
  96.             if (trie[node].nxt[c] == -1) {
  97.                 trie[node].nxt[c] = trie.size();
  98.                 trie.emplace_back();
  99.             }
  100.             node = trie[node].nxt[c];
  101.         }
  102.  
  103.         trie[node].pal.push_back(idx);
  104.         trie[node].word = idx;
  105.     }
  106.  
  107.     long long ans = 0;
  108.  
  109.     // Searching
  110.     for (int i = 0; i < n; ++i) {
  111.         const string &w = a[i];
  112.         int node = 0;
  113.         int L = w.size();
  114.  
  115.         for (int j = 0; j < L; ++j) {
  116.  
  117.             if (trie[node].word != -1 && trie[node].word != i
  118.                 && H[i].isPal(j, L-1)) {
  119.                 ans++;
  120.             }
  121.  
  122.             int c = w[j] - 'a';
  123.             if (trie[node].nxt[c] == -1) {
  124.                 node = -1;
  125.                 break;
  126.             }
  127.             node = trie[node].nxt[c];
  128.         }
  129.  
  130.         if (node != -1) {
  131.             for (int idx : trie[node].pal) {
  132.                 if (idx != i)
  133.                     ans++;
  134.             }
  135.         }
  136.     }
  137.  
  138.     cout << ans << "\n";
  139.     return 0;
  140. }
  141.  
Success #stdin #stdout 0.04s 5284KB
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https://ideone.com/rnQ7j7
language:
C++14 (gcc 8.3)
created:
6 days ago
visibility:
public

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