【HDOJ】3553 Just a String

后缀数组加二分可解。

 /* 3553 */
 #include <iostream>
 #include <sstream>
 #include <string>
 #include <map>
 #include <queue>
 #include <set>
 #include <stack>
 #include <vector>
 #include <deque>
 #include <algorithm>
 #include <cstdio>
 #include <cmath>
 #include <ctime>
 #include <cstring>
 #include <climits>
 #include <cctype>
 #include <cassert>
 #include <functional>
 #include <iterator>
 #include <iomanip>
 using namespace std;
 //#pragma comment(linker,"/STACK:102400000,1024000")

 #define sti                set<int>
 #define stpii            set<pair<int, int> >
 #define mpii            map<int,int>
 #define vi                vector<int>
 #define pii                pair<int,int>
 #define vpii            vector<pair<int,int> >
 #define rep(i, a, n)     for (int i=a;i<n;++i)
 #define per(i, a, n)     for (int i=n-1;i>=a;--i)
 #define clr                clear
 #define pb                 push_back
 #define mp                 make_pair
 #define fir                first
 #define sec                second
 #define all(x)             (x).begin(),(x).end()
 #define SZ(x)             ((int)(x).size())
 #define lson            l, mid, rt<<1
 #define rson            mid+1, r, rt<<1|1

 const int maxl = ;
 const int maxn = maxl;
 int a[maxn*];
 int rrank[maxn], height[maxn], sa[maxn*];
 int wa[maxn], wb[maxn], wc[maxn], wv[maxn];
 int dp[maxn][];
 __int64 tot[maxn];
 char s[maxl];
 __int64 kth;

 bool c0(int *r, int a, int b) {
     return r[a]==r[b] && r[a+]==r[b+] && r[a+]==r[b+];
 }

 bool c12(int k, int *r, int a, int b) {
     if (k == )
         return r[a]<r[b] || (r[a]==r[b] && c12(, r, a+, b+));
     else
         return r[a]<r[b] || (r[a]==r[b] && wv[a+]<wv[b+]);
 }

 void sort(int *r, int *a, int *b, int n, int m) {
     int i;

     for (i=; i<n; ++i) wv[i] = r[a[i]];
     for (i=; i<m; ++i) wc[i] = ;
     for (i=; i<n; ++i) wc[wv[i]]++;
     for (i=; i<m; ++i) wc[i] += wc[i-];
     for (i=n-; i>=; --i) b[--wc[wv[i]]] = a[i];
 }

 #define F(x) ((x)/3 + ((x)%3==1 ? 0:tb))
 #define G(x) ((x)<tb ? (x)*3+1 : ((x)-tb)*3+2)
 void dc3(int *r, int *sa, int n, int m) {
     int i, j, *rn=r+n, *san=sa+n, ta=, tb=(n+)/, tbc=, p;

     r[n] = r[n+] = ;
     for (i=; i<n; ++i) if (i%!=) wa[tbc++] = i;
     sort(r+, wa, wb, tbc, m);
     sort(r+, wb, wa, tbc, m);
     sort(r, wa, wb, tbc, m);
     for (p=, rn[F(wb[])]=, i=; i<tbc; ++i)
         rn[F(wb[i])] = c0(r, wb[i-], wb[i]) ? p- : p++;
     if (p < tbc)
         dc3(rn, san, tbc, p);
     else
         for (i=; i<tbc; ++i) san[rn[i]] = i;
     for (i=; i<tbc; ++i)
         if (san[i] < tb)
             wb[ta++] = san[i] * ;
     if (n% == )
         wb[ta++] = n - ;
     sort(r, wb, wa, ta, m);
     for (i=; i<tbc; ++i) wv[wb[i]=G(san[i])] = i;
     for (i=,j=,p=; i<ta && j<tbc; ++p)
         sa[p] = c12(wb[j]%, r, wa[i], wb[j]) ? wa[i++] : wb[j++];
     while (i < ta) sa[p++] = wa[i++];
     while (j < tbc) sa[p++] = wb[j++];
 }

 void calheight(int *r, int *sa, int n) {
     int i, j, k = ;

     for (i=; i<=n; ++i) rrank[sa[i]] = i;
     for (i=; i<n; height[rrank[i++]]=k)
     for (k?k--:, j=sa[rrank[i]-]; r[j+k]==r[i+k]; ++k) ;
 }

 void init_RMQ(int n) {
     int i, j;

     for (i=; i<=n; ++i) dp[i][] = i;
     for (j=; (<<j)<=n; ++j)
         for (i=; i+(<<j)-<=n; ++i)
             if (height[dp[i][j-]] < height[dp[i+(<<(j-))][j-]])
                 dp[i][j] = dp[i][j-];
             else
                 dp[i][j] = dp[i+(<<(j-))][j-];
 }

 int RMQ(int l, int r) {
     if (l > r)
         swap(l, r);

     ++l;
     int k = ;

     while (<<(k+) <= r-l+)
         ++k;

     if (height[dp[l][k]] < height[dp[r-(<<k)+][k]])
         return dp[l][k];
     else
         return dp[r-(<<k)+][k];
 }

 void printSa(int n) {
     for (int i=; i<=n; ++i)
         printf("%d ", sa[i]);
     putchar('\n');
 }

 void printHeight(int n) {
     for (int i=; i<=n; ++i)
         printf("%d ", height[i]);
     putchar('\n');
 }

 void solve() {
     int n = ;

     for (int i=; ; ++i) {
         if (s[i] == '\0') {
             n = i;
             break;
         }
         a[i] = s[i];
     }
     a[n] = ;

     dc3(a, sa, n+, );
     calheight(a, sa, n);
     init_RMQ(n);

     rep(i, , n+)
         tot[i] = tot[i-] + n - sa[i];

     int l = , r = n, mid, idx;
     int pre = ;
     int pos = , len;
     __int64 tmp;

     while (l < r) {
         idx = RMQ(l, r);
         mid = idx - ;
         tmp = 1LL * (height[idx] - pre) * (r-l+);
         if (kth <= tmp) {
             pos = l;
             len = pre + (kth+r-l)/(r-l+);
             break;
         }
         kth -= tmp;
         tmp = tot[mid] - tot[l-] - 1LL * height[idx] * (mid-l+);
         if (kth <= tmp) {
             r = mid;
         } else {
             kth -= tmp;
             l = mid + ;
         }
         pre = height[idx];
     }

     if (pos == ) {
         pos = l;
         len = pre + kth;
     }

     rep(i, , len)
         putchar(s[sa[pos]+i]);
     putchar('\n');
 }

 int main() {
     ios::sync_with_stdio(false);
     #ifndef ONLINE_JUDGE
         freopen("data.in", "r", stdin);
         freopen("data.out", "w", stdout);
     #endif

     int t;

     scanf("%d", &t);
     rep(tt, , t+) {
         scanf("%s %I64d", s, &kth);
         printf("Case %d: ", tt);
         solve();
     }

     #ifndef ONLINE_JUDGE
         printf("time = %d.\n", (int)clock());
     #endif

     return ;
 }

数据生成器。

 from random import randint, shuffle
 import shutil
 import string

 def GenDataIn():
     with open("data.in", "w") as fout:
         t = 20
         bound = 10**3
         uc = list(string.uppercase)
         fout.write("%d\n" % (t))
         for tt in xrange(t):
             n = randint(100, 200)
             kth = randint(1, n*(n+1)/2)
             line = ""
             for i in xrange(n):
                 idx = randint(0, 25)
                 line += uc[idx]
             fout.write("%s %d\n" % (line, kth))

 def MovDataIn():
     desFileName = "F:\eclipse_prj\workspace\hdoj\data.in"
     shutil.copyfile("data.in", desFileName)

 if __name__ == "__main__":
     GenDataIn()
     MovDataIn()