spoj 1812 Longest Common Substring II（后缀自动机）

代码

#include <cstdio>
#include <cstring>
#include <algorithm>

using namespace std;
typedef long long ll;
const int maxn = 100005;
const int SIGMA_SIZE = 26;
const int inf = 0x3f3f3f3f;

struct SAM {
int sz, last;
int g[maxn<<1][SIGMA_SIZE], pre[maxn<<1], step[maxn<<1];
int lcs[maxn<<1], tlcs[maxn<<1];

void newNode(int s) {
step[++sz] = s;
pre[sz] = 0;
lcs[sz] = s;
memset(g[sz], 0, sizeof(g[sz]));
}

int idx(char ch) { return ch -'a'; }

void init() {
sz = 0, last = 1;
newNode(0);
memset(tlcs, 0, sizeof(tlcs));
}

void insert(char ch) {
newNode(step[last] + 1);
int v = idx(ch), p = last, np = sz;

while (p && !g[p][v]) {
g[p][v] = np;
p = pre[p];
}

if (p) {
int q = g[p][v];
if (step[q] == step[p] + 1)
pre[np] = q;
else {
newNode(step[p] + 1);
int nq = sz;
for (int j = 0; j < SIGMA_SIZE; j++) g[nq][j] = g[q][j];

pre[nq] = pre[q];
pre[np] = pre[q] = nq;

while (p && g[p][v] == q) {
g[p][v] = nq;
p = pre[p];
}
}
} else
pre[np] = 1;
last = np;
}

void match(char* str) {
memset(tlcs, 0 , sizeof(tlcs));
int n = strlen(str), p = 1, ans = 0;
for (int i = 0; i < n; i++) {
int v = idx(str[i]);
if (g[p][v]) p = g[p][v], ans++;
else {
while (p && g[p][v] == 0) p = pre[p];
if (p) ans = step[p] + 1, p = g[p][v];
else ans = 0, p = 1;
}

tlcs[p] = max(tlcs[p], ans);
}
for (int i = 0; i < sz; i++) {
int u = id[i];
lcs[u] = min(lcs[u], tlcs[u]);
int v = pre[u];
//printf("%d %d %d!", u, v, tlcs[u]);
tlcs[v] = max(tlcs[v], tlcs[u]);
}
//printf("\n");
}

int solve() {
int ans = 0;
for (int i = 1; i <= sz; i++) {
//printf("%d ", lcs[i]);
ans = max(ans, lcs[i]);
}
//printf("\n");
return ans;
}

int du[maxn<<1], id[maxn<<1];
void topu() {
memset(du, 0, sizeof(du));
for (int i = 1; i <= sz; i++)
du[pre[i]]++;

int head = 0, rear = 0;
for (int i = 1; i <= sz; i++)
if (du[i] == 0) id[rear++] = i;

while (head < rear) {
int u = id[head++];
du[pre[u]]--;
if (du[pre[u]] == 0 && pre[u])
id[rear++] = pre[u];
}
}
}SA;

char str[20][maxn];

int main () {
int N = 0;
while (gets(str
) != NULL) N++;

SA.init();
int len = strlen(str[0]);
for (int i = 0; i < len; i++) SA.insert(str[0][i]);

SA.topu();
for (int i = 1; i < N; i++) SA.match(str[i]);
printf("%d\n", SA.solve());
return 0;
}