zoukankan      html  css  js  c++  java
  • SPOJ 7258 Lexicographical Substring Search

    Little Daniel loves to play with strings! He always finds different ways to have fun with strings! Knowing that, his friend Kinan decided to test his skills so he gave him a string S and asked him Q questions of the form:


    If all distinct substrings of string S were sorted lexicographically, which one will be the K-th smallest?


    After knowing the huge number of questions Kinan will ask, Daniel figured out that he can't do this alone. Daniel, of course, knows your exceptional programming skills, so he asked you to write him a program which given S will answer Kinan's questions.

    Example:


    S = "aaa" (without quotes)
    substrings of S are "a" , "a" , "a" , "aa" , "aa" , "aaa". The sorted list of substrings will be:
    "a", "aa", "aaa".

    Input

    In the first line there is Kinan's string S (with length no more than 90000 characters). It contains only small letters of English alphabet. The second line contains a single integer Q (Q <= 500) , the number of questions Daniel will be asked. In the next Q lines a single integer K is given (0 < K < 2^31).

    Output

    Output consists of Q lines, the i-th contains a string which is the answer to the i-th asked question.

    Example

    Input:
    aaa
    2
    2
    3

    Output: aa
    aaa

    题解:
    这题磨人啊,SPOJ跑的又慢,时限又短,压了一晚上常。
    思路如下:
    SAM满足性质:dfs序每一步走出来的都是一个子串,且满足从小到大顺序,关键满足不重不漏.
    那么根据性质可以想出:沿着SAM走k步就是k-th子串了.
    考虑优化:
    记录size[x]为x节点往下可以产生的子串个数,和上题类似可以拓扑序搞出来 然后如果小于rk那么就直接减去即可.
    压常技巧:
    1.rg inline 不解释
    2.不知为何,代码中k的输入写在函数内就快了4倍 懂得可以评论下....
     1 #include <algorithm>
     2 #include <iostream>
     3 #include <cstdlib>
     4 #include <cstring>
     5 #include <cstdio>
     6 #include <cmath>
     7 #define RG register
     8 using namespace std;
     9 const int N=90005,M=300005;
    10 char s[M];int n=0,cnt=1,last=1,cur=1,fa[M],ch[M][27],dis[M],size[M];
    11 void build(int c){
    12     last=cur;cur=++cnt;
    13     int p=last;
    14     dis[cur]=++n;
    15     for(;p && !ch[p][c];p=fa[p])ch[p][c]=cur;
    16     if(!p)fa[cur]=1;
    17     else{
    18         int q=ch[p][c];
    19         if(dis[q]==dis[p]+1)fa[cur]=q;
    20         else{
    21             int nt=++cnt;
    22             dis[nt]=dis[p]+1;
    23             memcpy(ch[nt],ch[q],sizeof(ch[q]));
    24             fa[nt]=fa[q];fa[q]=fa[cur]=nt;
    25             for(;ch[p][c]==q;p=fa[p])ch[p][c]=nt;
    26         }
    27     }
    28 }
    29 int sa[M];int c[M];
    30 void Flr(){
    31     int p;
    32     for(RG int i=1;i<=cnt;i++)c[dis[i]]++;
    33     for(RG int i=1;i<=n;i++)c[i]+=c[i-1];
    34     for(RG int i=cnt;i;i--)sa[c[dis[i]]--]=i;
    35     for(RG int i=cnt;i;i--){
    36         p=sa[i];
    37         size[p]=1;
    38         for(int j=0;j<=25;j++)
    39         size[p]+=size[ch[p][j]];
    40     }
    41 }
    42 void dfs(){
    43     RG int u,x=1,rk;
    44     scanf("%d",&rk);
    45     while(rk)
    46     {
    47         for(int i=0;i<=25;i++){
    48             u=ch[x][i];
    49             if(!u)continue;
    50             if(size[u]>=rk){
    51                 putchar('a'+i);
    52                 x=u;rk--;break;
    53             }
    54              else rk-=size[u];
    55         }
    56     }
    57     puts("");
    58 }
    59 void work(){
    60     scanf("%s",s);
    61     for(RG int i=0,l=strlen(s);i<l;i++)build(s[i]-'a');
    62     Flr();
    63     int Q,x;
    64     scanf("%d",&Q);
    65     while(Q--)dfs();
    66 }
    67 int main()
    68 {
    69     work();
    70     return 0;
    71 }
    
    
    


  • 相关阅读:
    iOS 9正式版开始推送 升级机型非常广泛
    dataWithContentsOfURL报错问题
    Android double输出时保留两位小数
    cornerstone忽略显示.DS_Store文件
    Couldn't open file on client side, trying server side 错误解决
    @SuppressWarnings有什么用处?
    iOS下UITableView的单元格重用逻辑
    根据滑动显隐状态栏的iOS实现
    Runloop之个人理解
    聚合支付概念
  • 原文地址:https://www.cnblogs.com/Yuzao/p/7271794.html
Copyright © 2011-2022 走看看