字典序第 k 大

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沿著自動機的邊走即可，比較水的一道題吧.

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Code:

#include <cstdio> #include <algorithm> #include <cstring> #define maxn 1000000 #define N 30 #define setIO(s) freopen(s".in","r",stdin) using namespace std; char str[maxn]; int opt,kth,n; struct SAM{int tot,last;int ch[maxn][N],f[maxn],cnt[maxn],mx[maxn],C[maxn],rk[maxn],sumv[maxn]; void init(){tot=last=1;}void ins(int c) {int np = ++tot,p = last; last = np; mx[np] = mx[p] + 1;while(p && !ch[p][c]) ch[p][c] = np,p = f[p];if(!p) f[np] = 1;else {int q = ch[p][c];if(mx[q] == mx[p] + 1) f[np] = q;else {int nq = ++tot;f[nq] = f[q]; f[q] = f[np] = nq; mx[nq] = mx[p] + 1;memcpy(ch[nq], ch[q], sizeof(ch[q])); while(p && ch[p][c] == q) ch[p][c] = nq, p = f[p]; }}cnt[np] = 1; }void Solve() {for(int i = 1;i <= tot; ++i) ++C[mx[i]];for(int i = 1;i <= tot; ++i) C[i] += C[i - 1]; for(int i = 1;i <= tot; ++i) rk[C[mx[i]]--] = i; for(int i = tot;i >= 1; --i) { int p = rk[i];if(opt == 1) cnt[f[p]] += cnt[p], sumv[p] = cnt[p]; else sumv[p] = cnt[p] = 1; for(int i = 0;i < 29; ++i) sumv[p] += sumv[ch[p][i]]; }}char ans[maxn]; int id; void BFS(int k) {cnt[1] = sumv[1] = 0; int p = 1,con = 1,flag2 = 1; while(con && flag2) {int flag = 1;flag2 = 0; for(int i = 0;i < 29; ++i) {if(flag == 1) {flag = 0; if(k <= cnt[p]) {con = 0; break;}else k -= cnt[p]; }//printf("%d %d\n",k,p);if(k > sumv[ch[p][i]]) k -= sumv[ch[p][i]];else { ans[++id] = i + 'a',flag2 = 1, p = ch[p][i]; break; }} }if(!con) {for(int i = 1;i <= id; ++i) printf("%c",ans[i]); }else printf("-1"); } }T; int main(){//setIO("input");T.init(),scanf("%s",str),n = strlen(str); for(int i = 0;i < n; ++i) T.ins(str[i] - 'a'); scanf("%d",&opt),T.Solve(),scanf("%d",&kth),T.BFS(kth); return 0; }

　　

轉載于:https://www.cnblogs.com/guangheli/p/10319721.html

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