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

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];
}
}