POJ - 1743 后缀自动机

POJ - 1743

顺着原字符串找到所有叶子节点，然后自下而上更新，每个节点right的最左和最右，然后求出答案。

#include<cstdio>
#include<cstring>
#include<algorithm>
#define LL long long
#define fi first
#define se second
#define mk make_pair
#define PII pair<int, int>
#define PLI pair<LL, int>
#define PDD pair<double,double>
#define ull unsigned long long
using namespace std;

const int N = 20000 + 7;
const int inf = 0x3f3f3f3f;
const LL INF = 0x3f3f3f3f3f3f3f3f;
const int mod = 1e9 + 7;
const double eps = 1e-8;
const int base = 87;

int n;
int s[N], a[N];

struct SuffixAutomaton {
    int last, cur, cnt, ch[N<<1][175], id[N<<1], fa[N<<1], dis[N<<1], sz[N<<1], c[N];
    int mx[N<<1], mn[N<<1];
    SuffixAutomaton() {cur = cnt = 1;}
    void init() {
        for(int i = 1; i <= cnt; i++) {
            memset(ch[i], 0, sizeof(ch[i]));
            sz[i] = c[i] = dis[i] = fa[i] = 0;
        }
        cur = cnt = 1;
    }
    void extend(int c, int id) {
        last = cur; cur = ++cnt;
        int p = last; dis[cur] = id;
        for(; p && !ch[p][c]; p = fa[p]) ch[p][c] = cur;
        if(!p) fa[cur] = 1;
        else {
            int q = ch[p][c];
            if(dis[q] == dis[p]+1) fa[cur] = q;
            else {
                int nt = ++cnt; dis[nt] = dis[p]+1;
                memcpy(ch[nt], ch[q], sizeof(ch[q]));
                fa[nt] = fa[q]; fa[q] = fa[cur] = nt;
                for(; ch[p][c]==q; p=fa[p]) ch[p][c] = nt;
            }
        }
        sz[cur] = 1;
    }
    void getSize(int n) {
        for(int i = 1; i <= cnt; i++) c[dis[i]]++;
        for(int i = 1; i <= n; i++) c[i] += c[i-1];
        for(int i = cnt; i >= 1; i--) id[c[dis[i]]--] = i;
        for(int i = cnt; i >= 1; i--) {
            int p = id[i];
            sz[fa[p]] += sz[p];
        }
    }
    void solve(int *s, int n) {
        memset(mx, 0, sizeof(int)*(cnt+1));
        memset(mn, inf, sizeof(int)*(cnt+1));
        for(int i = 1, p = 1; i <= n; i++) {
            p = ch[p][s[i]];
            mx[p] = mn[p] = i;
        }
        for(int i = cnt; i >= 1; i--) {
            int p = id[i];
            mx[fa[p]] = max(mx[fa[p]], mx[p]);
            mn[fa[p]] = min(mn[fa[p]], mn[p]);
        }
        int ans = 0;
        for(int i = 2; i <= cnt; i++) {
            ans = max(ans, min(mx[i]-mn[i], dis[i]));
        }
        if(ans < 4) puts("0");
        else printf("%d\n", ans+1);
    }
} sam;

int main() {
    while(scanf("%d", &n) != EOF && n) {
        sam.init();
        for(int i = 1; i <= n; i++) scanf("%d", &a[i]);
        for(int i = 1; i < n; i++) s[i] = a[i+1]-a[i]+base;
        for(int i = 1; i < n; i++) sam.extend(s[i], i);
        sam.getSize(n-1);
        sam.solve(s, n-1);
    }
    return 0;
}

/*
*/