【UVa 1592】Database

最新推荐文章于 2025-09-13 19:07:06 发布

转载最新推荐文章于 2025-09-13 19:07:06 发布 · 53 阅读

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原文链接：http://www.cnblogs.com/albert7xie/p/4732249.html

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#数据库 #人工智能

本文探讨了关系数据库中的冗余问题，并介绍了一种新的正常形式——Peter's Normal Form (PNF)，用于减少数据库中的数据冗余。通过示例说明如何判断一个表格是否符合PNF，并提供了一个检测算法。

Peter studies the theory of relational databases. Table in the relational database consists of values that are arranged in rows and columns.

There are different normal forms that database may adhere to. Normal forms are designed to minimize the redundancy of data in the database. For example, a database table for a library might have a row for each book and columns for book name, book author, and author's email.

If the same author wrote several books, then this representation is clearly redundant. To formally define this kind of redundancy Peter has introduced his own normal form. A table is in Peter's Normal Form (PNF) if and only if there is no pair of rows and a pair of columns such that the values in the corresponding columns are the same for both rows.

How to compete in ACM ICPC	Peter	peter@neerc.ifmo.ru
How to win ACM ICPC	Michael	michael@neerc.ifmo.ru
Notes from ACM ICPC champion	Michael	michael@neerc.ifmo.ru

The above table is clearly not in PNF, since values for 2rd and 3rd columns repeat in 2nd and 3rd rows. However, if we introduce unique author identifier and split this table into two tables -- one containing book name and author id, and the other containing book id, author name, and author email, then both resulting tables will be in PNF.

$\textstyle \parbox{.5\textwidth}{ \begin{center} \begin{tabular}{\vert l\vert l... ...\hline Notes from ACM ICPC champion & 2 \\ \hline \end{tabular} \end{center}}$ $\textstyle \parbox{.49\textwidth}{ \begin{center} \begin{tabular}{\vert l\vert ... ...ine 2 & Michael & michael@neerc.ifmo.ru \\ \hline \end{tabular} \end{center}}$

Given a table your task is to figure out whether it is in PNF or not.

Input

Input contains several datasets. The first line of each dataset contains two integer numbers n and m ( 1 $\le$ n $\le$ 10000, 1 $\le$ m $\le$ 10), the number of rows and columns in the table. The following n lines contain table rows. Each row has m column values separated by commas. Column values consist of ASCII characters from space (ASCII code 32) to tilde (ASCII code 126) with the exception of comma (ASCII code 44). Values are not empty and have no leading and trailing spaces. Each row has at most 80 characters (including separating commas).

Output

For each dataset, if the table is in PNF write to the output file a single word ``YES" (without quotes). If the table is not in PNF, then write three lines. On the first line write a single word ``NO" (without quotes). On the second line write two integer row numbers r₁ and r₂ ( 1 $\le$ r₁, r₂ $\le$ n, r₁ $\ne$ r₂), on the third line write two integer column numbers c₁ and c₂ ( 1 $\le$ c₁, c₂ $\le$ m, c1 $\ne$ c2), so that values in columns c₁ and c₂are the same in rows r₁ and r₂.

Sample Input

3 3
How to compete in ACM ICPC,Peter,peter@neerc.ifmo.ru
How to win ACM ICPC,Michael,michael@neerc.ifmo.ru
Notes from ACM ICPC champion,Michael,michael@neerc.ifmo.ru
2 3
1,Peter,peter@neerc.ifmo.ru
2,Michael,michael@neerc.ifmo.ru

Sample Output

NO
2 3
2 3
YES

首先有几个问题要注意一下。
fgets是读到回车并停止的，所以前面不能有回车。
要给每一个字符串分配一个编号。
接下来就是枚举+MAP判重了。

#include<cstdio>
#include<cstring>
#include<map>
#include<string>
#include<algorithm>
using namespace std;

struct hash
{
    int a[2];
    
    bool operator < (const hash &b) const
    {
        return a[0] < b.a[0] || (a[0] == b.a[0] && a[1] < b.a[1]);
    }
    
    bool operator == (const hash &b) const
    {
        return a[0] == b.a[0] && a[1] == b.a[1];
    }
};
int r;
int c;
map<string, int> idcard;
map<hash, int> app;
int table[10005][15];
int note;

void print()
{
    for (int i = 0; i < c; ++i)
        for (int j = i + 1; j < c; ++j)
        {
            app.clear();
            for (int k = 0; k < r; ++k)
            {
                hash dou;
                dou.a[0] = table[k][i];
                dou.a[1] = table[k][j];
                if (app.count(dou))
                {
                    printf("NO\n");
                    printf("%d %d\n", app[dou] + 1, k + 1);
                    printf("%d %d\n", i + 1, j + 1);
                    return;
                    
                }
                else
                {
                    app[dou] = k;
                }
            }
        }
    printf("YES\n");
}

int ID(string x)
{
    if (idcard.count(x)) return idcard[x];
    return idcard[x] = note++;
}

int main()
{
    while (scanf("%d %d", &r, &c) == 2)
    {
        char s[100];
        idcard.clear();
        note = 0;
        getchar();
        for (int i = 0; i < r; ++i)
        {
            fgets(s, 85, stdin);
            int k = 0;
            int len = strlen(s);
            string word = "";
            for (int j = 0; j < c; ++j)
            {
                while (k < len - 1 && s[k] != ',')
                    word += s[k++];
                table[i][j] = ID(word);
                word = "";
                ++k;
            }
        }
        print();
    }
    return 0;
}

转载于:https://www.cnblogs.com/albert7xie/p/4732249.html