【HDUoj】5635 - LCP Array（思维）

#include<cstdio>
#include<iostream>
#include<cstring>
#include<cmath>
#include<algorithm>
using namespace std;
typedef long long LL;
#define PI acos(-1.0)
#define INF 0x3f3f3f3f
#define CLR(a,b) memset(a,b,sizeof(a))
const LL mod = 1e9+7;
LL num[100000+5];
int main()
{
    int u;
    int n;
    num[0] = 0;
    cin >> u;
    while (u--)
    {
        cin >> n;
        bool flag = true;
        for (int i = 1 ; i < n ; i++)
        {
            cin >> num[i];
            if (num[i] > n-i)
                flag = false;
            else if (num[i-1] != 0 && num[i] != num[i-1] - 1)
                flag = false;
        }
        if (flag)
        {
            LL ans = 26;
            for (int i = 1 ; i < n ; i++)
            {
                if (!num[i]) 
                    ans = ans * 25 % mod;
            }
            cout << ans << endl;
        }
        else
            puts("0");
    }
    return 0;
}