题目大意

找一个环串的起点，使得从其开始遍历字典序最小

题解

建立后缀自动机，从根开始走length步，走到的点就是这个最小串的结尾，其step即表示它在串中的位置

step - n + 1即为开始位置

#include
    
     #include
     
      #include
      
       #include
       
        #include
        
         #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)#define BUG(s,n) for (int i = 1; i <= (n); i++) cout<
         
          <<' '; puts("");#define cls(x) memset(x,0,sizeof(x))using namespace std;const int maxn = 40005,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],step[maxn],ch[maxn][26],cnt,last,n;char s[maxn];void ins(int x){ int p = last,np = ++cnt; cls(ch[np]); 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 solve(){ int u = 1; REP(i,n) for (int j = 0; j < 26; j++) if (ch[u][j]){u = ch[u][j]; break;} printf("%d\n",step[u] - n + 1);}int main(){ int T = read(); while (T--){ scanf("%s",s + 1); n = strlen(s + 1); last = cnt = 1; memset(ch[1],0,sizeof(ch[1])); REP(i,n) ins(s[i] - 'a'); REP(i,n) ins(s[i] - 'a'); solve(); } return 0;}