POJ 1094-Sorting It All Out（拓扑排序）

Sorting It All Out

Time Limit: 1000MS Memory Limit: 10000KTotal Submissions: 28055 Accepted: 9689

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 6A<BA<CB<CC<DB<DA<B3 2A<BB<A26 1A<Z0 0

Sample Output

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

每输入一条边就要用拓扑排序判断一次，如果有环则输出有环，如果多解则继续输入，如果排序已完成则输出排序结果。

#include <stdio.h>#include <string.h>#include <math.h>#include <stdlib.h>#include <iostream>#include <algorithm>#include <vector>#include <stack>using namespace std;int n, m,in[30],cnt,ma[30][30];char ans[30];int top_sort(){stack <int> s;int flag = 0;    cnt=0;    memset(in,0,sizeof(in));    for(int i=1;i<=n;i++)        for(int j=1;j<=n;j++)        if(ma[i][j])        in[j]++;for (int i = 1; i <= n; i++)if (in[i] == 0){s.push(i);}while (!s.empty()){if (s.size() > 1){flag = 1;}int u = s.top();s.pop();ans[cnt++] = u - 1 + 'A';for (int i = 1; i <=n; i++){if(ma[u][i]){    in[i]--;    if(in[i]==0)                    s.push(i);}}}if (cnt < n){return 0;}elseif (flag == 1){return 1;}else{return 2;}}int main(){char c[5];while (~scanf("%d%d", &n, &m)){if (!m && !n){break;}int ok = 1;memset(ma,0,sizeof(ma));for (int i = 1; i <= m; i++){scanf("%s", c);if(!ok)continue;int u = c[2] - 'A' + 1, v = c[0] - 'A' + 1;ma[u][v]=1;int x = top_sort();if (x == 2){printf("Sorted sequence determined after %d relations: ", i);for (int i = cnt - 1; i >= 0; i--){printf("%c", ans[i]);}printf(".\n");ok = 0;}elseif (x == 0){printf("Inconsistency found after %d relations.\n", i);ok = 0;}}if (ok){printf("Sorted sequence cannot be determined.\n");}}return 0;}