【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 = 100005;
const int maxn = maxl;
int a[maxn*3];
int rrank[maxn], height[maxn], sa[maxn*3];
int wa[maxn], wb[maxn], wc[maxn], wv[maxn];
int dp[maxn][17];
__int64 tot[maxn];
char s[maxl];
__int64 kth;

bool c0(int *r, int a, int b) {
    return r[a]==r[b] && r[a+1]==r[b+1] && r[a+2]==r[b+2];
}

bool c12(int k, int *r, int a, int b) {
    if (k == 2)
        return r[a]<r[b] || (r[a]==r[b] && c12(1, r, a+1, b+1));
    else
        return r[a]<r[b] || (r[a]==r[b] && wv[a+1]<wv[b+1]);
}

void sort(int *r, int *a, int *b, int n, int m) {
    int i;
    
    for (i=0; i<n; ++i) wv[i] = r[a[i]];
    for (i=0; i<m; ++i) wc[i] = 0;
    for (i=0; i<n; ++i) wc[wv[i]]++;
    for (i=1; i<m; ++i) wc[i] += wc[i-1];
    for (i=n-1; i>=0; --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=0, tb=(n+1)/3, tbc=0, p;
    
    r[n] = r[n+1] = 0;
    for (i=0; i<n; ++i) if (i%3!=0) wa[tbc++] = i;
    sort(r+2, wa, wb, tbc, m);
    sort(r+1, wb, wa, tbc, m);
    sort(r, wa, wb, tbc, m);
    for (p=1, rn[F(wb[0])]=0, i=1; i<tbc; ++i)
        rn[F(wb[i])] = c0(r, wb[i-1], wb[i]) ? p-1 : p++;
    if (p < tbc)
        dc3(rn, san, tbc, p);
    else
        for (i=0; i<tbc; ++i) san[rn[i]] = i;
    for (i=0; i<tbc; ++i)
        if (san[i] < tb)
            wb[ta++] = san[i] * 3;
    if (n%3 == 1)
        wb[ta++] = n - 1;
    sort(r, wb, wa, ta, m);
    for (i=0; i<tbc; ++i) wv[wb[i]=G(san[i])] = i;
    for (i=0,j=0,p=0; i<ta && j<tbc; ++p)
        sa[p] = c12(wb[j]%3, 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 = 0;
    
    for (i=1; i<=n; ++i) rrank[sa[i]] = i;
    for (i=0; i<n; height[rrank[i++]]=k)
    for (k?k--:0, j=sa[rrank[i]-1]; r[j+k]==r[i+k]; ++k) ;
}

void init_RMQ(int n) {
    int i, j;
    
    for (i=1; i<=n; ++i) dp[i][0] = i;
    for (j=1; (1<<j)<=n; ++j)
        for (i=1; i+(1<<j)-1<=n; ++i)
            if (height[dp[i][j-1]] < height[dp[i+(1<<(j-1))][j-1]])
                dp[i][j] = dp[i][j-1];
            else
                dp[i][j] = dp[i+(1<<(j-1))][j-1];
}

int RMQ(int l, int r) {
    if (l > r)
        swap(l, r);
    
    ++l;
    int k = 0;
    
    while (1<<(k+1) <= r-l+1)
        ++k;
    
    if (height[dp[l][k]] < height[dp[r-(1<<k)+1][k]])
        return dp[l][k];
    else
        return dp[r-(1<<k)+1][k];
}

void printSa(int n) {
    for (int i=1; i<=n; ++i)
        printf("%d ", sa[i]);
    putchar('
');
}

void printHeight(int n) {
    for (int i=1; i<=n; ++i)
        printf("%d ", height[i]);
    putchar('
');
}

void solve() {
    int n = 0;
    
    for (int i=0; ; ++i) {
        if (s[i] == '') {
            n = i;
            break;
        }
        a[i] = s[i];
    }
    a[n] = 0;
    
    dc3(a, sa, n+1, 130);
    calheight(a, sa, n);
    init_RMQ(n);
    
    rep(i, 1, n+1)
        tot[i] = tot[i-1] + n - sa[i];
        
    int l = 1, r = n, mid, idx;
    int pre = 0;
    int pos = 0, len;
    __int64 tmp;
    
    while (l < r) {
        idx = RMQ(l, r);
        mid = idx - 1;
        tmp = 1LL * (height[idx] - pre) * (r-l+1);
        if (kth <= tmp) {
            pos = l;
            len = pre + (kth+r-l)/(r-l+1);
            break;
        }
        kth -= tmp;
        tmp = tot[mid] - tot[l-1] - 1LL * height[idx] * (mid-l+1);
        if (kth <= tmp) {
            r = mid;
        } else {
            kth -= tmp;
            l = mid + 1;
        }
        pre = height[idx];
    }
    
    if (pos == 0) {
        pos = l;
        len = pre + kth;
    }
    
    rep(i, 0, len)
        putchar(s[sa[pos]+i]);
    putchar('
');
}

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, 1, t+1) {
        scanf("%s %I64d", s, &kth);
        printf("Case %d: ", tt);
        solve();
    }
    
    #ifndef ONLINE_JUDGE
        printf("time = %d.
", (int)clock());
    #endif
    
    return 0;
}

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
" % (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
" % (line, kth))
                
def MovDataIn():
    desFileName = "F:eclipse_prjworkspacehdojdata.in"
    shutil.copyfile("data.in", desFileName)

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