VMSS '15 #0 - Head Data Slave Applications

Points: 10

Time limit: 1.0s

Memory limit: 256M

Authors:

JeffreyZ, LeoF

Problem type

Welcome to Massey CS Club 2015/16!

To start things off, a new head data slave needs to be hired (the old one has been promoted).

The new head data slave must not only be fast at copying data, but also decent with math calculations or simply bashing numbers. Luckily for most people, the head data slave exam only consists of 1 question. Solve this question for bonus (Komachi) points.

Question

In the massive multiplayer online role-playing game Elder Tale, the humans are at war with monsters. Shiroe, the strategist of the legendary Debauchery Tea Party is in charge of organizing $N$ $N$ $(1 \le N \le 500)$ $(1 \leq N \leq 500)$ NPC militants to fight. The armed forces consists of $K$ $K$ different kinds of militants. Each militant is labelled with a number $1$ $1$ to $K$ $K$ based on importance. Militants who share the same number are indistinguishable. Shiroe wants to know the number of ways he can organize his army in a line such that the last militant with number $i$ $i$ is before the last militant with number $i+1$ $i + 1$ for $(1 \le i \le K-1)$ $(1 \leq i \leq K - 1)$ .

Input Specification

The first line of input will have one integer $K$ $K$ $(1 \le K \le 500)$ $(1 \leq K \leq 500)$ , the number of different kinds of militants.
The following $K$ $K$ lines will contain one integer each. The $i^\text{th}$ $i^{th}$ line will contain $m_i$ $m_{i}$ $(1 \le m_i \le 500)$ $(1 \leq m_{i} \leq 500)$ , the number of militants with the number $i$ $i$ .

Output Specification

Print the number of ways Shiroe can order his armies modulo $1\,000\,000\,007$ $1 000 000 007$ .

Sample Input 1

Copy

Sample Output 1

Copy

Explanation

The 3 ways are:

1 1 2 2 3

1 2 1 2 3

2 1 1 2 3

Ah, that scored high Komachi points!

Sample Input 2

Copy

Sample Output 2

Copy

Comments

0

YouZ commented on Sept. 17, 2015, 8:11 p.m.

Leo I like Log Horizon and everything, but I don't get the input specifications. What are those integers supposed to mean????

0

nathanl3 commented on Sept. 20, 2015, 11:30 a.m. ← edited →

The given input is : 3 2 2 1

Which is interpreted as:

First line: There are 3 types of militants

Second line: There are 2 militants of type 1

Third line: There are 2 militants of type 2

Fourth line: There are 2 militants of type 3

For example, 1 1 2 2 3 is a valid case for this input