Codeforce-152C-Pocket Book(排列组合+思维)

C. Pocket Book
time limit per test:2 seconds
memory limit per test:256 megabytes
input:standard input
output:standard output

One day little Vasya found mom's pocket book. The book had n names of her friends and unusually enough, each name was exactly m letters long. Let's number the names from 1 to n in the order in which they are written.

As mom wasn't home, Vasya decided to play with names: he chose three integers i, j, k (1 ≤ i < j ≤ n, 1 ≤ k ≤ m), then he took names number i and j and swapped their prefixes of length k. For example, if we take names "CBDAD" and "AABRD" and swap their prefixes with the length of 3, the result will be names "AABAD" and "CBDRD".

You wonder how many different names Vasya can write instead of name number 1, if Vasya is allowed to perform any number of the described actions. As Vasya performs each action, he chooses numbers i, j, k independently from the previous moves and his choice is based entirely on his will. The sought number can be very large, so you should only find it modulo 1000000007 (109 + 7).

Input

The first input line contains two integers n and m (1 ≤ n, m ≤ 100) — the number of names and the length of each name, correspondingly. Then n lines contain names, each name consists of exactly m uppercase Latin letters.

Output

Print the single number — the number of different names that could end up in position number 1 in the pocket book after the applying the procedures described above. Print the number modulo 1000000007 (109 + 7).

Examples
Input
2 3
AAB
BAA
Output
4
Input
4 5
ABABA
BCGDG
AAAAA
YABSA
Output
216
Note

In the first sample Vasya can get the following names in the position number 1: "AAB", "AAA", "BAA" and "BAB".


题意:给出n个长度为m的字符串,任意两个字符串可以交换前k个字符(k<=m),交换后字符串变成新的字符串,问最后能产生多少个不同的字符串

思路:认真想一想可以发现,每个字符串的每一列都可以变成所有字符串的该列的字符,所以只要统计每一列有多少个不同的字符,然后排列组合就行

AC代码:

#include<iostream>
#include<cstring>
#include<cstdio>
#include<algorithm>
#include<queue>
#include<stack>
#include<map>
using namespace std;
char str[105][105];
int cnt[105];
int vis[26];
int n,m;
int main()
{
    while(~scanf("%d%d",&n,&m))
    {
        memset(cnt,0,sizeof(cnt));
        for(int i=1;i<=n;i++)
            scanf("%s",str[i]+1);
        for(int i=1;i<=m;i++){
            memset(vis,0,sizeof(vis));
            for(int j=1;j<=n;j++){
                if(vis[str[j][i]-'A']==0)cnt[i]++,vis[str[j][i]-'A']=1;
            }
        }
        long long ans=1;
        for(int i=1;i<=m;i++)
            ans=ans*cnt[i]%1000000007;
        printf("%lld\n",ans);
    }
    return 0;
}


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转载自blog.csdn.net/qq_37171272/article/details/78746086