POJ1743--Musical Theme

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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
题意:求最长不重叠的音段。首先得相邻作差。
PS:sa[0]就是末尾添加的0的位置。
#include <iostream>#include <cstdio>#include <cstring>#include <cmath>using namespace std;#define maxn 200080int key[maxn],str[maxn];int sa[maxn],t[maxn],t2[maxn],c[maxn];int height[maxn],Rank[maxn];void build_sa(int * s,int n,int m){int i,*x = t,*y = t2;for(i = 0;i < m;i++)c[i] = 0;for(i = 0;i < n;i++)c[ x[i] = s[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(int k = 1;k <= n;k <<= 1){int 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 = 0;i < m;i++)c[i] += c[i-1];for(i = n-1;i >= 0;i--)sa[--c[x[y[i]]]] = y[i];//根据sa和y数组计算新的x数组swap(x,y);p = 1;x[sa[0]] = 0;for(i = 1;i < n;i++)x[sa[i]] = y[sa[i-1]] == y[sa[i]] && y[sa[i-1] + k] == y[sa[i] + k] ? p-1:p++;if(p >= n)break;m = p;}}void getHeight(int * s,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--;int j = sa[Rank[i]-1];while(s[i+k] == s[j+k])k++;height[Rank[i]] = k;}}bool Judge(int n,int len){int Min = 0,Max = 0;for(int i = 1;i < n;i++){if(height[i] < len)Min = Max = sa[i];else {Min = min(Min,sa[i]);Max = max(Max,sa[i]);if(Max - Min >= len)return 1;}}return 0;}int main(){//freopen("in.txt","r",stdin);int n;while(scanf("%d",&n)!=EOF && n){for(int i = 0;i < n;i++)scanf("%d",&key[i]);if(n == 1){puts("0");continue;}for(int i = 0;i < n-1;i++)str[i] = key[i+1] - key[i] + 90;str[n-1] = 0;build_sa(str,n,180);getHeight(str,n);int l = 4,r = n/2;int ans = 0;while(l <= r){int mid = (l+r) >> 1;if(Judge(n,mid)){ans = mid;l = mid + 1;}else r = mid - 1;}if(ans < 4)puts("0");else printf("%d\n",ans+1);}return 0;}


	
				
		
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