♥HDOJ 5635-LCP Array

LCP Array

Time Limit: 4000/2000 MS (Java/Others)    Memory Limit: 131072/131072 K (Java/Others)

Total Submission(s): 159    Accepted Submission(s): 47

Problem Description

Peter has a string s=s1s2...sn, let suffi=sisi+1...sn be the suffix start with i-th character of s. Peter knows the lcp (longest common prefix) of each two adjacent suffixes which denotes asai=lcp(suffi,suffi+1)(1≤i<n).

Given the lcp array, Peter wants to know how many strings containing lowercase English letters only will satisfy the lcp array. The answer may be too large, just print it modulo109+7.

 

Input

There are multiple test cases. The first line of input contains an integerT indicating the number of test cases. For each test case:

The first line contains an integer n (2≤n≤105) -- the length of the string. The second line contains n−1 integers: a1,a2,...,an−1(0≤ai≤n).

The sum of values of n in all test cases doesn't exceed 106.

 

Output

For each test case output one integer denoting the answer. The answer must be printed modulo109+7.

 

Sample Input

330 043 2 131 2

 

Sample Output

16250260

 

Source

BestCoder Round #74 (div.2)

#include<stdio.h>#include<string.h>#include<algorithm>using namespace std;int a[1000000];int n;void f(){int i,j;long long ans=26;for(i=1;i<n;i++){if((a[i]-1)!=a[i+1]&&a[i]!=0){printf("0\n");return ;}}int uu=0;for(i=1;i<=n;i++){if(a[i]==0){if(uu>0){ans*=25;ans=ans%1000000007;}elseuu++;}}printf("%I64d\n",ans);}int main(){int t;scanf("%d",&t);while(t--){scanf("%d",&n);int i,j;for(i=1;i<n;i++){scanf("%d",&a[i]);}a[n]=0;f();}return 0;}