#1746. 【2022.11.8 联考】回文（palindrome）

https://sjzezoj.com/submission/64047

S2OJ/1746/1746.cpp

@@ -0,0 +1,101 @@
+#include <iostream>
+#include <algorithm>
+#include <string>
+#include <vector>
+
+using std::cin;
+using std::cout;
+const char endl = '\n';
+
+const int N = 300005;
+
+int q, st[N << 1][20];
+std::string s;
+
+std::vector<int> manacher(const std::string &_s) {
+    int n = _s.size();
+    std::string s(n * 2 + 3, '#');
+
+    for (int i = 0; i < n; i++) {
+        s[i * 2 + 2] = _s[i];
+    }
+
+    s[0] = '^';
+    s[n * 2 + 2] = '$';
+
+    std::vector<int> p(s.size(), 1);
+
+    for (int i = 1, mid = 0, r = 0; i <= n * 2 + 1; i++) {
+        p[i] = i < r ? std::min(p[mid * 2 - i], r - i) : 1;
+
+        while (s[i - p[i]] == s[i + p[i]]) p[i]++;
+
+        if (i + p[i] - 1 > r) {
+            r = i + p[i] - 1;
+            mid = i;
+        }
+    }
+
+    // for (int i = 0; i < n; i++) {
+    //     p[i] = p[i * 2 + 2] / 2;
+    // }
+
+    // p.resize(n);
+
+    return p;
+}
+
+int query(int l, int r) {
+    if (l > r) return 1;
+    int k = std::__lg(r - l + 1);
+    return std::max(st[l][k], st[r - (1 << k) + 1][k]);
+}
+
+int main() {
+    std::ios::sync_with_stdio(false);
+    cin.tie(nullptr);
+
+    cin >> s >> q;
+
+    auto p = manacher(s);
+    int n = s.size();
+    int t = std::__lg(p.size());
+
+    for (int i = 1; i <= p.size(); i++) {
+        st[i][0] = p[i - 1];
+    }
+
+    for (int i = 1; i <= t; i++) {
+        for (int j = 1; j <= p.size() - (1 << i) + 1; j++) {
+            st[j][i] = std::max(st[j][i - 1], st[j + (1 << (i - 1))][i - 1]);
+        }
+    }
+
+    while (q--) {
+        int ql, qr;
+
+        cin >> ql >> qr;
+
+        ql = (ql + 1) * 2 + 1;
+        qr = (qr + 1) * 2 + 1;
+
+        int l = 1,
+            r = qr - ql + 1,
+            res = 1;
+
+        while (l <= r) {
+            int mid = l + r >> 1;
+
+            if (query(ql + mid - 1, qr - mid + 1) - 1 >= mid) {
+                res = mid;
+                l = mid + 1;
+            } else {
+                r = mid - 1;
+            }
+        }
+
+        cout << res << endl;
+    }
+
+    return 0;
+}