POJ 1509 Glass Beads【字尾自動機、最小表示法】

此題為最簡單的字尾自動機的應用。

#include <iostream>
#include <cstring>
#include <cstdio>
#include <algorithm>
#include <cmath>

using namespace std;

const int maxn = 10010;

struct SamNode {
    int ch[26];
    int par, len;
    void Init() {
        par = -1;
        len = 0;
        memset(ch, -1, sizeof(ch));
    }
};

class SAM
{
public:
    void Init() {
        tot = 0;
        last = 0;
        sn[0].Init();
    }
    void Add(int c) {
        int end = NewNode();
        int tmp = last;
        sn[end].len = sn[last].len + 1;
        for ( ; tmp != -1 && sn[tmp].ch[c] == -1; tmp = sn[tmp].par) {
            sn[tmp].ch[c] = end;
        }
        if (tmp == -1) {
            sn[end].par = 0;
        } else {
            int nxt = sn[tmp].ch[c];
            if (sn[tmp].len + 1 == sn[nxt].len) {
                sn[end].par = nxt;
            } else {
                int np = NewNode();
                sn[np] = sn[nxt];
                sn[np].len = sn[tmp].len + 1;
                sn[end].par = sn[nxt].par = np;
                for ( ; tmp != -1 && sn[tmp].ch[c] == nxt; tmp = sn[tmp].par) {
                    sn[tmp].ch[c] = np;
                }
            }
        }
        last = end;
    }
    int tot;
    int last;
    SamNode sn[maxn*4];
    int NewNode() {
        sn[++tot].Init();
        return tot;
    }
};

int t, n;
char s[maxn];
SAM sam;

int main()
{
    scanf("%d", &t);
    while (t--) {
        scanf("%s", s);
        sam.Init();
        n = strlen(s);
        for (int i = 0; i < n; ++i) {
            sam.Add(s[i] - 'a');
        }
        for (int i = 0; i < n; ++i) {
            sam.Add(s[i] - 'a');
        }
        int now = 0;
        for (int i = 0; i < n; ++i) {
            for (int j = 0; j < 26; ++j) {
                if (sam.sn[now].ch[j] != -1) {
                    now = sam.sn[now].ch[j];
                    break;
                }
            }
        }
        printf("%d\n", sam.sn[now].len - n + 1);
    }
    return 0;
}