poj 1094 Sorting It All Out 【拓扑排序】
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Sorting It All Out
Time Limit: 1000MS Memory Limit: 10000KTotal Submissions: 29404 Accepted: 10184
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.
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.
费解。。。 得到拓扑序列 或者 成环没有拓扑序列 的优先级高于 无序。 题目意思是:只要在 当前输入的关系 可以得到拓扑序列 或者 成环 就直接输出answer 。
站在别人的肩膀上ac的。 第一道拓扑序列:
#include <cstdio>#include <cstring>#include <algorithm>using namespace std;int map[27][27];int in[27];//记录每个点的入度int mark[27];//存储每次查询时各点的入度 int topo[27];//存储序列值 int n, m;void trans()//传递每个节点的入度 { for(int i = 1; i <= n; i++) mark[i] = in[i];}int toposort(){ trans(); int i, j; int t = 0;//统计当前序列个数 int num;//统计当前入度为0的点的个数 int next;//数组 下一并入点 int judge = 1; for(i = 1; i <= n; i++) { num = 0; for(j = 1; j <= n; j++) { if(!mark[j])//入度为0 { num++; next = j; } } if(!num) //有环 查询失败 return 0; if(num > 1)//当前无序 这里只能标记不能返回 因为有可能在后面查询中会成环 若成环直接输出答案 judge = -1; //return -1; topo[t++] = next;//并入数组 //printf("%d\n", next); mark[next] = -1;//不再查询该点 for(j = 1; j <= n; j++)//更新操作 与并入点有关系的点入度全部减一 { if(map[next][j]) mark[j]--; } } return judge; //return 1;} void init(){ for(int i = 1; i <= n; i++) { in[i] = 0; for(int j = 1; j <= n; j++) { map[i][j] = 0; } }}int main(){ int i, j; int x, y; int sign;//标记是否查询出结果 int exist; char str[10]; while(scanf("%d%d", &n, &m),n||m) { init();//初始化 sign = 0;//若查询出结果标记为1 for(i = 1; i <= m; i++) { scanf("%s", str); if(sign) continue;//已有结果 下面的不用处理 x = str[0] - 'A' + 1; y = str[2] - 'A' + 1; map[x][y] = 1; in[y]++;//记录入度 exist = toposort(); if(exist == 1)//查询成功 { sign = 1;//已经查询出结果 printf("Sorted sequence determined after %d relations: ", i); for(j = 0; j < n; j++) { printf("%c", 'A'+topo[j]-1); } printf(".\n"); } else if(!exist) //矛盾 ->查询失败 { sign = 1;//已经有结果 printf("Inconsistency found after %d relations.\n", i); } } if(!sign) printf("Sorted sequence cannot be determined.\n"); } return 0;}
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