可算过了

这是道论文题。有相应的论文的。
主要想法是枚举长度，然后跳着遍历。
我这里维护了两个rmq，并且在后面又接了一个倒序的字符串
网上有人说不用这样，只要在往前遍历就好了。但我觉得这是错的，很可能会将复杂度提升到O(n^2)
所以，我维护了两个rmq
累死了，也没快多少

代码如下：

#include<iostream>
#include<algorithm>
#include<cstdio>
#include<cstring>
#include<cmath>
using namespace std;
const int max_n = 2e5 + 100;
char s[max_n];
//后缀数组模板.
//SA[i] 排名为i的后缀的起始坐标
//rank[i] 起始坐标为i的后缀的排名
//height[i]=k 表示SA[i-1]与SA[i]代表的后缀的最长公共前缀的长度为k
int a[max_n];
int ranks[max_n], SA[max_n], height[max_n];
int wa[max_n], wb[max_n], wvarr[max_n], wsarr[max_n];
inline int cmp(int* r, int a, int b, int l) {
    return r[a] == r[b] && r[a + l] == r[b + l];
}
inline void get_sa(int* r, int* sa, int n, int m) {
    //r:原数组
    //sa:SA
    //n:原数组长度
    //m:原数组种类数，用于基数排序
    ++n;
    int i, j, p, * x = wa, * y = wb, * t;
    for (i = 0; i < m; ++i) wsarr[i] = 0;
    for (i = 0; i < n; ++i) wsarr[x[i] = r[i]]++;
    for (i = 1; i < m; ++i) wsarr[i] += wsarr[i - 1];
    for (i = n - 1; i >= 0; --i) sa[--wsarr[x[i]]] = i;
    for (j = 1, p = 1; p < n; j <<= 1, m = p) {
        for (p = 0, i = n - j; i < n; ++i) y[p++] = i;
        for (i = 0; i < n; ++i) if (sa[i] >= j) y[p++] = sa[i] - j;
        for (i = 0; i < n; ++i) wvarr[i] = x[y[i]];
        for (i = 0; i < m; ++i) wsarr[i] = 0;
        for (i = 0; i < n; ++i) wsarr[wvarr[i]]++;
        for (i = 1; i < m; ++i) wsarr[i] += wsarr[i - 1];
        for (i = n - 1; i >= 0; --i) sa[--wsarr[wvarr[i]]] = y[i];
        for (t = x, x = y, y = t, p = 1, x[sa[0]] = 0, i = 1; i < n; ++i)
            x[sa[i]] = cmp(y, sa[i - 1], sa[i], j) ? p - 1 : p++;
    }
}//求解高度数组，height[i]指排名
void get_height(int* r, int* sa, int n) {
    int i, j, k = 0;
    for (i = 1; i <= n; ++i) ranks[sa[i]] = i;
    for (i = 0; i < n; height[ranks[i++]] = k)
        for (k ? k-- : 0, j = sa[ranks[i] - 1]; r[i + k] == r[j + k]; k++);
    return;
}
//后缀数组

//附加rmq_st 专门对后缀数组
int st[max_n][32];
int st2[max_n][32];
void initSt(int a[], int n) {
    for (int i = 0;i <= n;++i)st[i][0] = height[i];
    int mxk = (int)log2(n + 1);
    for (int k = 1;k <= mxk;++k) {
        for (int i = 0;i <= n;++i) {
            if (i + (1 << k) - 1 > n)break;
            st[i][k] = min(st[i][k - 1], st[i + (1 << (k - 1))][k - 1]);
        }
    }
    for (int i = 0;i <= n;++i)st2[i][0] = ranks[i];
    for (int k = 1;k <= mxk;++k) {
        for (int i = 0;i <= n;++i) {
            if (i + (1 << k) - 1 > n)break;
            st2[i][k] = min(st2[i][k - 1], st2[i + (1 << (k - 1))][k - 1]);
        }
    }
}
int que(int l, int r) {
    l = ranks[l];r = ranks[r];
    if (l > r)swap(l, r);
    ++l;
    int len = log2(r - l + 1);
    return min(st[l][len], st[r - (1 << len) + 1][len]);
}
int que2(int l,int r) {
    if (l > r)swap(l, r);
    int len = log2(r - l + 1);
    return min(st2[l][len], st2[r - (1 << len) + 1][len]);
}
int main() {
    ios::sync_with_stdio(0);
    int tcase = 0;
    while (cin >> s) {
        if (s[0] == '#')break;
        int n = strlen(s);
        for (int i = 0;i < n;++i)a[i] = s[i] - 'a' + 1;
        a[n] = 30;for (int i = n + 1;i < 2 * n + 1;++i)a[i] = a[2 * n - i];
        get_sa(a, SA, 2 * n + 1, 40);
        get_height(a, SA, 2 * n + 1);
        initSt(a, 2 * n + 1);
        int Max = 1;int ans = -1;int ll = 0;
        for (int len = 1;len <= n;++len) {
            for (int i = 0;i + len <= n;i += len) {
                if (a[i] != a[i + len])continue;
                int tmp_len = que(i, i + len);
                int res = tmp_len / len + 1;
                int tmp = tmp_len % len;
                int pos;
                int k = que(2 * n - i, 2 * n - (i + len)) - 1;
                if (k >= len - tmp) {
                    ++res;
                    int lft = max(i - k, i - len);
                    int rght = i - len + tmp;
                    pos = SA[que2(lft, rght)];
                }
                else {
                    int lft = i - k;
                    int rght = i;
                    pos = SA[que2(lft, rght)];
                }if (res > Max) {
                    Max = res;
                    ans = pos;
                    ll = len;
                }
                else if (res == Max && (ans == -1 || ranks[pos] < ranks[ans])) {
                    ans = pos;
                    ll = len;
                }
            }
        }
        if (Max == 1) {
            char ch = 'z';
            for (int i = 0;i < n;++i)ch = min(ch, s[i]);
            cout << "Case " << ++tcase << ": " << ch << endl;
        }
        else {
            cout << "Case " << ++tcase << ": ";
            for (int i = ans;i < ans + ll * Max;++i)cout << s[i];
            cout << endl;
        }
    }
}