spoj 7258 Lexicographical Substring Search（后缀数组 | 后缀自动机）

题目链接：spoj 7258 Lexicographical Substring Search

代码 - 后缀数组

#include <cstdio>
#include <cstring>
#include <stack>
#include <vector>
#include <algorithm>

using namespace std;
const int maxn = 90000 + 5;

struct Suffix_Arr {
    int n, s[maxn];
    int SA[maxn], rank[maxn], height[maxn];
    int tmp_one[maxn], tmp_two[maxn], c[305];

    void init(char* str);
    void build(int m);
    void get_height();

    int f[maxn];
    void solve();
    void query(char* str, int k);
}SFA;

char str[maxn];

int main () {
    scanf("%s", str);
    SFA.init(str);
    int q, k;
    SFA.solve();
    scanf("%d", &q);
    while (q--) {
        scanf("%d", &k);
        SFA.query(str, k);
    }
    return 0;
}

void Suffix_Arr::init(char* str) {
    n = 0;
    int len = strlen(str);
    for (int i = 0; i < len; i++)
        s[n++] = str[i];
    s[n++] = 0;
}
void Suffix_Arr::query(char* str, int k) {
    int idx = lower_bound(f, f + n, k) - f;
    int bw = k - f[idx-1] + height[idx], s = SA[idx];
    for (int i = 0; i < bw; i++)
        printf("%c", str[s+i]);
    printf("\n");
}

void Suffix_Arr::solve() {
    build(300);
    get_height();
    f[0] = 0;
    for (int i = 1; i < n; i++)
        f[i] = f[i-1] + (n - 1 - SA[i] - height[i]);
}

void Suffix_Arr::get_height() {
    for (int i = 0; i < n; i++)
        rank[SA[i]] = i;
    int mv = height[0] = 0;
    for (int i = 0; i < n - 1; i++) {
        if (mv) mv--;

        int j = SA[rank[i]-1];
        while (s[i+mv] == s[j+mv]) mv++;
        height[rank[i]] = mv;
    }
}

void Suffix_Arr::build(int m) {
    int* x = tmp_one, *y = tmp_two;

    for (int i = 0; i < m; i++) c[i] = 0;
    for (int i = 0; i < n; i++) c[x[i] = s[i]]++;
    for (int i = 1; i < m; i++) c[i] += c[i-1];
    for (int i = n - 1; i >= 0; i--) SA[--c[x[i]]] = i;

    for (int k = 1; k <= n; k <<= 1) {
        int mv = 0;
        for (int i = n - k; i < n; i++) y[mv++] = i;
        for (int i = 0; i < n; i++) if(SA[i] >= k) 
            y[mv++] = SA[i] - k;

        for (int i = 0; i < m; i++) c[i] = 0;
        for (int i = 0; i < n; i++) c[x[y[i]]]++;
        for (int i = 1; i < m; i++) c[i] += c[i-1];
        for (int i = n - 1; i >= 0; i--) SA[--c[x[y[i]]]] = y[i];

        swap(x, y);
        mv = 1;
        x[SA[0]] = 0;

        for (int i = 1; i < n; i++)
            x[SA[i]] = (y[SA[i-1]] == y[SA[i]] && y[SA[i-1] + k] == y[SA[i] + k] ? mv - 1 : mv++);

        if (mv >= n) break;
        m = mv;
    }
}

代码-后缀自动机

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

using namespace std;
typedef long long ll;
const int maxn = 90005; 
const int SIGMA_SIZE = 26;

struct SAM {
    int sz, last;
    int g[maxn<<1][SIGMA_SIZE], pre[maxn<<1], step[maxn<<1];
    int pos[maxn<<1], right[maxn<<1];
    ll cnt[maxn<<1];

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

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

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

    void insert(char ch);
    void get_tuopu();
    void get_right(char* str);

    void presolve() {
        get_tuopu();
        for (int i = 1; i <= sz; i++) cnt[i] = 1;
        for (int i = sz; i; i--) {
            int u = pos[i];
            for (int j = 0; j < SIGMA_SIZE; j++)
                cnt[u] += cnt[g[u][j]];
        }
    }
    void query(int k) {
        int p = 1;

        while (k) {
            k--;
            for (int i = 0; i < SIGMA_SIZE; i++) {
                int u = g[p][i];
                if (u == 0) continue;
                if (cnt[u] <= k) k -= cnt[u];
                else { printf("%c", i + 'a'); p = u; break; }
            }
        }
        printf("\n");

        /* for (int i = 1; i <= sz; i++) printf("%d %lld\n", i, cnt[i]); */
    }
}SA;

char str[maxn];

int main () {
    scanf("%s", str);
    int n = strlen(str), k;
    SA.init();
    for (int i = 0; i < n; i++) SA.insert(str[i]);
    SA.presolve();

    scanf("%d", &n);
    while (n--) {
        scanf("%d", &k);
        SA.query(k);
    }
    return 0;
}

void SAM::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 SAM::get_tuopu() {
    for (int i = 0; i <= sz; i++) cnt[i] = 0;
    for (int i = 1; i <= sz; i++) cnt[step[i]]++;
    for (int i = 1; i <= sz; i++) cnt[i] += cnt[i-1];
    for (int i = 1; i <= sz; i++) pos[cnt[step[i]]--] = i; 
}

void SAM::get_right(char* str) {
    int p = 1, n = strlen(str);
    for (int i = 0; i <= sz; i++) right[i] = 0;

    for (int i = 0; i < n; i++) {
        int v = idx(str[i]);
        p = g[p][v];
        right[p]++;
    }

    for (int i = sz; i; i--) {
        int u = pos[i];
        right[pre[u]] += right[u];
    }
}