poj-1094-Sorting It All Out
2015-12-09 17:48
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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.
A<B
A<C
B<C
C<D
B<D
A<B
3 2
A<B
B<A
26 1
A<Z
0 0
Inconsistency found after 2 relations.
Sorted sequence cannot be determined.
拓扑排序问题
该题题意明确,就是给定一组字母的大小关系判断他们是否能组成唯一的拓扑序列。是典型的拓扑排序,但输出格式上确有三种形式:
1. 该字母序列有序,并依次输出;
2. 该序列不能判断是否有序;
3. 该序列字母次序之间有矛盾,即有环存在。
而这三种形式的判断是有顺序的:先判断是否有环(3),再判断是否有序(1),最后才能判断是否能得出结果(2)。注意:对于(2)必须遍历完整个图,而(1)和(3)一旦得出结果,对后面的输入就不用做处理了。
代码:
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<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.
拓扑排序问题
该题题意明确,就是给定一组字母的大小关系判断他们是否能组成唯一的拓扑序列。是典型的拓扑排序,但输出格式上确有三种形式:
1. 该字母序列有序,并依次输出;
2. 该序列不能判断是否有序;
3. 该序列字母次序之间有矛盾,即有环存在。
而这三种形式的判断是有顺序的:先判断是否有环(3),再判断是否有序(1),最后才能判断是否能得出结果(2)。注意:对于(2)必须遍历完整个图,而(1)和(3)一旦得出结果,对后面的输入就不用做处理了。
代码:
[code]#include <iostream> #include <cmath> #include <cstdio> #include <iomanip> #include <cstring> #include <string> #include <stack> #include <queue> const int N = 30; using namespace std; int map , in , n, m, q[27]; char alp ; int toposort() { int tmp , i, t, a, p = 0, res = 1; stack<int> q; a = 0; for (i = 0; i < n; i++) { tmp[i] = in[i]; if (!tmp[i]) { q.push(i); a++; } } while(!q.empty()) { if (q.size() > 1) res = -1; t = q.top(); alp[p++] = t+'A'; q.pop(); for (i = 0; i < n; i++) { if (map[t][i]) { tmp[i]--; if (!tmp[i]) { q.push(i); } } } } alp[p] = 0; if (p != n) return 0; return res; } int main() { #ifndef ONLINE_JUDGE freopen("1.txt", "r", stdin); #endif int i, j, ans, sign; string str; while(cin >> n >> m && n) { memset(map, 0, sizeof(map)); memset(in, 0, sizeof(in)); sign = 0; for (i = 1; i <= m; i++) { cin >> str; if(sign) continue; map[str[0]-'A'][str[2]-'A'] = 1; in[str[2]-'A']++; ans = toposort(); if (ans == 0) { cout << "Inconsistency found after " << i << " relations." << endl; sign = 1; } else if (ans == 1) { cout << "Sorted sequence determined after " << i << " relations: " << alp << ".\n"; sign = 1; } } if (!sign) { cout << "Sorted sequence cannot be determined.\n"; } } return 0; }
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