题目

求第K小子串

题解

建好SAM后，拓扑排序，反向传递后面所形成的串的数量
最后从根开始，按照儿子形成串的数量与k比较走就好了

#include<iostream>
#include<cmath>
#include<cstdio>
#include<cstring>
#include<algorithm>
#define LL long long int
#define REP(i,n) for (int i = 1; i <= (n); i++)
#define Redge(u) for (int k = h[u],to; k; k = ed[k].nxt)
using namespace std;
const int maxn = 200005,maxm = 100005,INF = 1000000000;
inline int read(){int out = 0,flag = 1; char c = getchar();while (c < 48 || c > 57) {if (c == '-') flag = -1; c = getchar();}while (c >= 48 && c <= 57) {out = (out << 3) + (out << 1) + c - '0'; c = getchar();}return out * flag;
}
int pre[maxn],sz[maxn],step[maxn],ch[maxn][26],cnt,last,n;
int a[maxn],b[maxn];
char s[maxn];
void ins(int x){int p = last,np = ++cnt;last = np; step[np] = step[p] + 1;while (p && !ch[p][x]) ch[p][x] = np,p = pre[p];if (!p) pre[np] = 1;else {int q = ch[p][x];if (step[q] == step[p] + 1) pre[np] = q;else {int nq = ++cnt; step[nq] = step[p] + 1;for (int i = 0; i < 26; i++) ch[nq][i] = ch[q][i];pre[nq] = pre[q]; pre[np] = pre[q] = nq;while (ch[p][x] == q) ch[p][x] = nq,p = pre[p];}}
}
void walk(int k){int u = 1;while (k){for (int i = 0; i < 26; i++) if (ch[u][i]){if (sz[ch[u][i]] >= k){putchar(i + 'a');k--; u = ch[u][i];break;}else k -= sz[ch[u][i]];}}puts("");
}
void solve(){REP(i,cnt) b[step[i]]++;REP(i,cnt) b[i] += b[i - 1];REP(i,cnt) a[b[step[i]]--] = i;for (int i = cnt; i; i--){int u = a[i]; sz[u] = 1;for (int j = 0; j < 26; j++)if (ch[u][j]) sz[u] += sz[ch[u][j]];}int Q = read();while (Q--) walk(read());
}
int main(){scanf("%s",s + 1);n = strlen(s + 1); cnt = last = 1;REP(i,n) ins(s[i] - 'a');solve();return 0;
}