POJ 1743 后缀数组+分组二分

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Musical Theme
Time Limit: 1000MS Memory Limit: 30000KTotal Submissions: 16365 Accepted: 5636

Description

A musical melody is represented as a sequence of N (1<=N<=20000)notes that are integers in the range 1..88, each representing a key on the piano. It is unfortunate but true that this representation of melodies ignores the notion of musical timing; but, this programming task is about notes and not timings.
Many composers structure their music around a repeating &qout;theme&qout;, which, being a subsequence of an entire melody, is a sequence of integers in our representation. A subsequence of a melody is a theme if it:
  • is at least five notes long
  • appears (potentially transposed -- see below) again somewhere else in the piece of music
  • is disjoint from (i.e., non-overlapping with) at least one of its other appearance(s)

Transposed means that a constant positive or negative value is added to every note value in the theme subsequence.
Given a melody, compute the length (number of notes) of the longest theme.
One second time limit for this problem's solutions!

Input

The input contains several test cases. The first line of each test case contains the integer N. The following n integers represent the sequence of notes.
The last test case is followed by one zero.

Output

For each test case, the output file should contain a single line with a single integer that represents the length of the longest theme. If there are no themes, output 0.

Sample Input

3025 27 30 34 39 45 52 60 69 79 69 60 52 45 39 34 30 26 22 1882 78 74 70 66 67 64 60 65 800

Sample Output

5后缀数组简单应用,求出sa,rank,height数组,然后二分答案,判断可行性。代码:
/* ***********************************************Author :xianxingwuguanCreated Time :2014-1-27 10:57:50File Name :1.cpp************************************************ */#pragma comment(linker, "/STACK:102400000,102400000")#include <stdio.h>#include <string.h>#include <iostream>#include <algorithm>#include <vector>#include <queue>#include <set>#include <map>#include <string>#include <math.h>#include <stdlib.h>#include <time.h>using namespace std;const int maxn=600010;/* *   sa 数组: 排第几的是谁 *   rank数组:谁排第几。 *   height[i]:sa[i],sa[i-1]的最长公共前缀。 * */int str[maxn],sa[maxn],rank[maxn],height[maxn],t1[maxn],t2[maxn],c[maxn];void da(int *str,int n,int m){      int i,j,k,p,*x=t1,*y=t2;      for(i=0;i<m;i++)c[i]=0;      for(i=0;i<n;i++)c[x[i]=str[i]]++;      for(i=1;i<m;i++)c[i]+=c[i-1];      for(i=n-1;i>=0;i--)sa[--c[x[i]]]=i;      for(k=1;k<=n;k<<=1)      {     p=0;     for(i=n-k;i<n;i++)y[p++]=i;     for(i=0;i<n;i++)if(sa[i]>=k)y[p++]=sa[i]-k;     for(i=0;i<m;i++)c[i]=0;     for(i=0;i<n;i++)c[x[y[i]]]++;     for(i=1;i<m;i++)c[i]+=c[i-1];     for(i=n-1;i>=0;i--)sa[--c[x[y[i]]]]=y[i];     swap(x,y);     x[sa[0]]=0;     p=1;     for(i=1;i<n;i++)     x[sa[i]]=y[sa[i]]==y[sa[i-1]]&&y[sa[i]+k]==y[sa[i-1]+k]?p-1:p++;     if(p>=n)break;     m=p;      }}void calheight(int *str,int n){      int i,j,k=0;      for(i=0;i<=n;i++)rank[sa[i]]=i;      for(i=0;i<n;i++)      {     if(k)k--;     j=sa[rank[i]-1];     while(str[i+k]==str[j+k])k++;     height[rank[i]]=k;      }}bool judge(int *sa,int n,int k){      int i,mx=sa[1],mn=sa[1];      for(i=2;i<=n;i++)      {     if(height[i]<k)mx=mn=sa[i];     else      {    if(sa[i]<mn)mn=sa[i];    if(sa[i]>mx)mx=sa[i];    if(mx-mn>k)return 1;     }      }      return 0;}int main(){      //freopen("data.in","r",stdin);      //freopen("data.out","w",stdout);      int i,j,k,m,n;      while(~scanf("%d",&n)&&n)      {     scanf("%d",&j);     for(i=0;i<n-1;i++)     {    scanf("%d",&k);    str[i]=k-j+100;    j=k;     }     str[n-1]=0;     da(str,n,200);     calheight(str,n-1);     int l=1,r=n/2;     while(l<r)     {   m=(l+r+1)>>1;   if(!judge(sa,n-1,m))r=m-1;   else l=m;     }     if(l>=4)l++;else l=0;     printf("%d\n",l);           }      return 0;}


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