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

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题目链接：spoj 1812 Longest Common Substring II
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[N]) != 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;}
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