poj 1094 Sorting It All Out (拓扑排序)

Sorting It All Out

Time Limit: 1000MS   Memory Limit: 10000K
Total Submissions: 27929   Accepted: 9655

Description

An ascending sorted sequence of distinct values is one in which some form of a less-than operator is used to order the elements from smallest to largest. For example, the sorted sequence A, B, C, D implies that A < B, B < C and C < D. in this problem, we will
give you a set of relations of the form A < B and ask you to determine whether a sorted order has been specified or not.

Input

Input consists of multiple problem instances. Each instance starts with a line containing two positive integers n and m. the first value indicated the number of objects to sort, where 2 <= n <= 26. The objects to be sorted will be the first n characters of
the uppercase alphabet. The second value m indicates the number of relations of the form A < B which will be given in this problem instance. Next will be m lines, each containing one such relation consisting of three characters: an uppercase letter, the character
"<" and a second uppercase letter. No letter will be outside the range of the first n letters of the alphabet. Values of n = m = 0 indicate end of input.

Output

For each problem instance, output consists of one line. This line should be one of the following three:

Sorted sequence determined after xxx relations: yyy...y.

Sorted sequence cannot be determined.

Inconsistency found after xxx relations.

where xxx is the number of relations processed at the time either a sorted sequence is determined or an inconsistency is found, whichever comes first, and yyy...y is the sorted, ascending sequence.

Sample Input

4 6
A<B
A<C
B<C
C<D
B<D
A<B
3 2
A<B
B<A
26 1
A<Z
0 0

Sample Output

Sorted sequence determined after 4 relations: ABCD.
Inconsistency found after 2 relations.
Sorted sequence cannot be determined.

思路:根据矛盾优先原则,即只要出现矛盾就结束程序,输出答案;然后再没有矛盾的基础上进行拓扑排序看能否得出它们之间关系;最后,若以上两者均没有结果,则是条件不足。同时,我们要输入一个关系进行一次判断。

在程序中,每次拓扑后若满足合法的拓扑条件,就记录答案。最后判断是否有矛盾关系即可。

#include"stdio.h"
#include"string.h"
#include"vector"
#include"queue"
#include"iostream"
#include"algorithm"
using namespace std;
#define N 1000
#define M 26
vector<int>g[M];     //记录拓扑关系
int pre[M],n,m,flag,t;
int mark[M];        标记字符是否出现及是否使用过
char ans[M+5];      记录答案
void top_sort(int k)
{
    t=k+1;
    int i,j,u,v,tmp;
    queue<int>q;
    memset(pre,0,sizeof(pre));
    memset(mark,0,sizeof(mark));
    for(i=0;i<n;i++)
    {
        if(g[i].size()!=0)
            mark[i]=1;        //等于1代表该字符出现
        for(j=0;j<g[i].size();j++)
        {
            v=g[i][j];
            mark[v]=1;
            pre[v]++;
        }
    }
    j=0;
    while(1)
    {
        tmp=0;
        for(i=0;i<n;i++)
        {
            if(pre[i]==0&&mark[i]==1)
            {
                mark[i]=-1;      //字符已经用过一次
                u=i;
                q.push(u);
                tmp++;
            }
        }
        if(tmp==0)       //排序结束标志
            break;
        else if(tmp==1) //条件合法,记录答案
            ans[j++]='A'+u-0;
        while(!q.empty())
        {
            u=q.front();
            q.pop();
            for(i=0;i<g[u].size();i++)
            {
                v=g[u][i];
                pre[v]--;
            }
        }
    }
    for(tmp=i=0;i<n;i++)
        if(pre[i])
            tmp++;
    if(tmp>0)      //出现该情况肯定是出现矛盾
        flag=2;
    else if(j==n)
        flag=1;
    ans[j]='\0';
}
int main()
{
    char s[10];
    int i,u,v;
    while(scanf("%d%d",&n,&m),n||m)
    {
        flag=0;
        for(i=0;i<M;i++)
            g[i].clear();
        for(i=0;i<m;i++)
        {
            scanf("%s",s);
            if(!flag)
            {
                u=s[0]-'A';
                v=s[2]-'A';
                g[u].push_back(v);
                top_sort(i);        //进行拓扑排序
            }
        }
        if(flag==1)
            printf("Sorted sequence determined after %d relations: %s.\n",t,ans);
        else if(flag==2)
            printf("Inconsistency found after %d relations.\n",t);
        else
            printf("Sorted sequence cannot be determined.\n");
    }
    return 0;
}
时间: 2024-10-05 12:21:21

poj 1094 Sorting It All Out (拓扑排序)的相关文章

POJ 1094 Sorting It All Out 拓扑排序

Sorting It All Out Time Limit:1000MS     Memory Limit:10000KB     64bit IO Format:%lld & %llu Description An ascending sorted sequence of distinct values is one in which some form of a less-than operator is used to order the elements from smallest to

拓扑序列变形 之 poj 1094 Sorting It All Out

/* 拓扑序列变形 之 poj 1094 Sorting It All Out 变形: 在每消去唯一一个入度为0的点后,只剩下唯一一个入度为0的点. 这样获得的n个点才是排序好的. */ 1 #include <iostream> 2 #include <cstdlib> 3 #include <cstdio> 4 #include <cstddef> 5 #include <iterator> 6 #include <algorithm&

poj 1094 Sorting It All Out 解题报告

题目链接:http://poj.org/problem?id=1094 题目意思:给出 n 个待排序的字母 和 m 种关系,问需要读到第 几 行可以确定这些字母的排列顺序或者有矛盾的地方,又或者虽然具体的字母顺序不能确定但至少不矛盾.这些关系均是这样的一种形式: 字母1 < 字母2 这道题目属于图论上的拓扑排序,由于要知道读入第几行可以确定具体的顺序,所以每次读入都需要进行拓扑排序来检验,这时每个点的入度就需要存储起来,所以就有了代码中memcpy 的使用了. 拓扑排序的思路很容易理解,但写起来

POJ 2367:Genealogical tree(拓扑排序)

Genealogical tree Time Limit: 1000MS Memory Limit: 65536K Total Submissions: 2738 Accepted: 1838 Special Judge Description The system of Martians' blood relations is confusing enough. Actually, Martians bud when they want and where they want. They ga

POJ 1128 &amp; ZOJ 1083 Frame Stacking (拓扑排序)

http://acm.zju.edu.cn/onlinejudge/showProblem.do?problemId=83 http://poj.org/problem?id=1128 Frame Stacking Time Limit: 1000MS   Memory Limit: 10000K Total Submissions: 4102   Accepted: 1378 Description Consider the following 5 picture frames placed

[ACM] POJ 1094 Sorting It All Out (拓扑排序)

Sorting It All Out Time Limit: 1000MS   Memory Limit: 10000K Total Submissions: 26801   Accepted: 9248 Description An ascending sorted sequence of distinct values is one in which some form of a less-than operator is used to order the elements from sm

POJ 1094 Sorting It All Out【floyd传递闭包+拓扑排序】

Sorting It All Out Time Limit: 1000MS Memory Limit: 10000K Total Submissions: 31994 Accepted: 11117 Description An ascending sorted sequence of distinct values is one in which some form of a less-than operator is used to order the elements from small

POJ 1094 Sorting It All Out(拓扑排序&#183;判断+实现)

题意  由一些不同元素组成的升序序列是可以用若干个小于号将所有的元素按从小到大的顺序 排列起来的序列.例如,排序后的序列为 A, B, C, D,这意味着 A < B.B < C和C < D.在本题中, 给定一组形如 A < B的关系式,你的任务是判定是否存在一个有序序列. 输出到哪一项可以确定顺序或者在这一项最先出现冲突,若所有的小于关系都处理完了都不能确定顺序也没有出现冲突,就输出不能确定 每来一个小于关系就进行一次拓扑排序  直到出现冲突(也就是出现了环)或者已经能确定顺序

poj 1094 Sorting It All Out 拓补排序

Description An ascending sorted sequence of distinct values is one in which some form of a less-than operator is used to order the elements from smallest to largest. For example, the sorted sequence A, B, C, D implies that A < B, B < C and C < D.