Sha 12206-stammering aliens (suffix array)

Ultraviolet A 12206-stammering aliens

Question Link

Given a sequence, find the maximum subscript of the substring that appears more than m and has the longest length.

Idea: suffix array. After the height array is created, you can use binary to search for it.

This topic can be written in hash format before, but when I write an array with a suffix, I made a silly mistake and failed to output none to node... This is the second time that I encountered such a teasing mistake. I still need to pay attention to it ..

Code:

#include <cstdio>#include <cstring>#include <algorithm>using namespace std;const int MAXLEN = 40005;struct Suffix {    int s[MAXLEN];    int sa[MAXLEN], t[MAXLEN], t2[MAXLEN], c[MAXLEN], n;    int rank[MAXLEN], height[MAXLEN];    void build_sa(int m) {n++;int i, *x = t, *y = t2;for (i = 0; i < m; i++) c[i] = 0;for (i = 0; i < n; i++) c[x[i] = s[i]]++;for (i = 1; i < m; i++) c[i] += c[i - 1];for (i = n - 1; i >= 0; i--) sa[--c[x[i]]] = i;for (int k = 1; k <= n; k <<= 1) {    int p = 0;    for (i = n - k; i < n; i++) y[p++] = i;    for (i = 0; i < n; i++) if (sa[i] >= k) y[p++] = sa[i] - k;    for (i = 0; i < m; i++) c[i] = 0;    for (i = 0; i < n; i++) c[x[y[i]]]++;    for (i = 0; i < m; i++) c[i] += c[i - 1];    for (i = n - 1; i >= 0; i--) sa[--c[x[y[i]]]] = y[i];    swap(x, y);    p = 1; x[sa[0]] = 0;    for (i = 1; i < n; i++)x[sa[i]] = (y[sa[i - 1]] == y[sa[i]] && y[sa[i - 1] + k] == y[sa[i] + k]) ? p - 1 : p++;    if (p >= n) break;    m = p;}n--;    }    void getHeight() {int i, j, k = 0;for (i = 1; i <= n; i++) rank[sa[i]] = i;for (i = 0; i < n; i++) {    if (k) k--;    int j = sa[rank[i] - 1];    while (s[i + k] == s[j + k]) k++;    height[rank[i]] = k;}    }} gao;const int N = 40005;int m;char str[N];int judge(int x) {    int ans = -1;    for (int i = 1; i <= gao.n; i++) {if (gao.n - gao.sa[i] < x) continue;int Max = gao.sa[i], cnt = 1;while (gao.height[i + 1] >= x && i < gao.n) {    Max = max(Max, gao.sa[i + 1]);    cnt++;    i++;}if (cnt >= m)    ans = max(ans, Max);    }    return ans;}void solve() {    if (judge(1) == -1) {printf("none\n");return;    }    int l = 1, r = gao.n - m + 2;    while (l < r) {int mid = (l + r) / 2;if (judge(mid) != -1) l = mid + 1;else r = mid;    }    l--;    printf("%d %d\n", l, judge(l));}int main() {    while (~scanf("%d", &m) && m) {scanf("%s", str);int len = strlen(str);for (int i = 0; i < len; i++)    gao.s[i] = str[i] - 'a' + 1;gao.s[len] = 0;gao.n = len;gao.build_sa(27);gao.getHeight();solve();    }    return 0;}