[whu1564]后缀树组

  1 #pragma comment(linker, "/STACK:10240000,10240000")
  2 
  3 #include <iostream>
  4 #include <cstdio>
  5 #include <algorithm>
  6 #include <cstdlib>
  7 #include <cstring>
  8 #include <map>
  9 #include <queue>
 10 #include <deque>
 11 #include <cmath>
 12 #include <vector>
 13 #include <ctime>
 14 #include <cctype>
 15 #include <set>
 16 #include <bitset>
 17 #include <functional>
 18 #include <numeric>
 19 #include <stdexcept>
 20 #include <utility>
 21 
 22 using namespace std;
 23 
 24 #define mem0(a) memset(a, 0, sizeof(a))
 25 #define mem_1(a) memset(a, -1, sizeof(a))
 26 #define lson l, m, rt << 1
 27 #define rson m + 1, r, rt << 1 | 1
 28 #define define_m int m = (l + r) >> 1
 29 #define rep_up0(a, b) for (int a = 0; a < (b); a++)
 30 #define rep_up1(a, b) for (int a = 1; a <= (b); a++)
 31 #define rep_down0(a, b) for (int a = b - 1; a >= 0; a--)
 32 #define rep_down1(a, b) for (int a = b; a > 0; a--)
 33 #define all(a) (a).begin(), (a).end()
 34 #define lowbit(x) ((x) & (-(x)))
 35 #define constructInt4(name, a, b, c, d) name(int a = 0, int b = 0, int c = 0, int d = 0): a(a), b(b), c(c), d(d) {}
 36 #define constructInt3(name, a, b, c) name(int a = 0, int b = 0, int c = 0): a(a), b(b), c(c) {}
 37 #define constructInt2(name, a, b) name(int a = 0, int b = 0): a(a), b(b) {}
 38 #define pchr(a) putchar(a)
 39 #define pstr(a) printf("%s", a)
 40 #define sstr(a) scanf("%s", a)
 41 #define sint(a) scanf("%d", &a)
 42 #define sint2(a, b) scanf("%d%d", &a, &b)
 43 #define sint3(a, b, c) scanf("%d%d%d", &a, &b, &c)
 44 #define pint(a) printf("%d\n", a)
 45 #define test_print1(a) cout << "var1 = " << a << endl
 46 #define test_print2(a, b) cout << "var1 = " << a << ", var2 = " << b << endl
 47 #define test_print3(a, b, c) cout << "var1 = " << a << ", var2 = " << b << ", var3 = " << c << endl
 48 
 49 typedef double db;
 50 typedef long long LL;
 51 typedef pair<int, int> pii;
 52 typedef multiset<int> msi;
 53 typedef set<int> si;
 54 typedef vector<int> vi;
 55 typedef map<int, int> mii;
 56 
 57 const int dx[8] = {0, 0, -1, 1, 1, 1, -1, -1};
 58 const int dy[8] = {-1, 1, 0, 0, 1, -1, 1, -1 };
 59 const int maxn = 1e6 + 7;
 60 const int md = 1e9 + 7;
 61 const int inf = 1e9 + 7;
 62 const LL inf_L = 1e18 + 7;
 63 const double pi = acos(-1.0);
 64 const double eps = 1e-6;
 65 
 66 template<class T>T gcd(T a, T b){return b==0?a:gcd(b,a%b);}
 67 template<class T>bool max_update(T &a,const T &b){if(b>a){a = b; return true;}return false;}
 68 template<class T>bool min_update(T &a,const T &b){if(b<a){a = b; return true;}return false;}
 69 template<class T>T condition(bool f, T a, T b){return f?a:b;}
 70 template<class T>void copy_arr(T a[], T b[], int n){rep_up0(i,n)a[i]=b[i];}
 71 int make_id(int x, int y, int n) { return x * n + y; }
 72 
 73 
 74 /// 构造后缀数组的之前，需要在原串末尾加个空字符(比其它字符都小即可)，
 75 ///把这个空字符看成原串的一部分（这样在比较的时候到这个位置一定可以分个大小）,
 76 ///所以n应该为原序列长度+1，后缀n-1是"空串"，sa[0]总是n-1。
 77 struct SuffixArray {
 78     int n;
 79     int arr[6][maxn];
 80     int *sa, *x, *y, *c, *rnk, *height;
 81     SuffixArray() { sa = arr[0]; x = arr[1]; y = arr[2]; c = arr[3]; rnk = arr[4]; height = arr[5]; }
 82     void resize(int nn) {  n = nn; mem0(arr[0]); }
 83     void build_sa(int s[], int m) { // m is biger than the max value of char
 84         rep_up0(i, m) c[i] = 0;
 85         rep_up0(i, n) c[x[i] = s[i]]++;
 86         rep_up1(i, m - 1) c[i] += c[i - 1];
 87         rep_down0(i, n) sa[--c[x[i]]] = i;
 88         for (int k = 1; k <= n; k <<= 1) {
 89             int p = 0;
 90             for (int i = n - k; i < n; i++) y[p++] = i;
 91             rep_up0(i, n) if (sa[i] >= k) y[p++] = sa[i] - k;
 92             rep_up0(i, m) c[i] = 0;
 93             rep_up0(i, n) c[x[y[i]]]++;
 94             rep_up0(i, m) c[i] += c[i - 1];
 95             rep_down0(i, n) sa[--c[x[y[i]]]] = y[i];
 96             swap(x, y);
 97             p = 1; x[sa[0]] = 0;
 98             for (int i = 1; i < n; i++) {
 99                 x[sa[i]] = y[sa[i - 1]] == y[sa[i]] && y[sa[i - 1] + k] == y[sa[i] + k]? p - 1 : p++;
100             }
101             if (p >= n) break;
102             m = p;
103         }
104     }
105     void build_height(int s[]) {
106         int k = 0;
107         rep_up0(i, n) rnk[sa[i]] = i;
108         rep_up0(i, n) {
109             if (k) k--;
110             int j = sa[rnk[i] - 1];
111             while (s[i + k] == s[j + k]) k++;
112             height[rnk[i]] = k;
113         }
114     }
115 };
116 
117 SuffixArray sa;
118 char s[maxn];
119 int ss[maxn];
120 
121 int main() {
122     //freopen("in.txt", "r", stdin);
123     int n, k;
124     while (cin >> n >> k) {
125         scanf("%s", s);
126         rep_up0(i, n) ss[i + n] = ss[i] = s[i];
127         ss[2 * n] = 0;
128         int len = n * 2 + 1;
129         sa.resize(len);
130         sa.build_sa(ss, 128);
131         int cnt = 0;
132         for (int i = 1; i < len; i++) {
133             if (sa.sa[i] < n) {
134                 cnt++;
135                 if (cnt == k) {
136                     int x = sa.sa[i];
137                     if (x == 0) x = n;
138                     cout << x << endl;
139                     break;
140                 }
141             }
142         }
143     }
144     return 0;
145 }