pku 1094 Sorting It All Out 拓扑排序

最新推荐文章于 2017-08-09 20:47:00 发布

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本文介绍了一种基于邻接矩阵实现的拓扑排序算法，并通过具体实例展示了如何使用该算法来解决排序问题。讨论了如何检测图中是否存在回路以及如何确定排序是否可以进行。

#include <iostream> #include <stack> using namespace std; int edge[27][27]; //图的邻接矩阵 int in_degree[27]; //顶点的入度 bool flagDegree[27]; char strRet[27]; int n, m; //拓扑排序 //-1: 继续 //0: 完成排序 //1: 有回路 int TopoOrder() { stack<int> s; memset(in_degree, 0, sizeof(in_degree)); memset(strRet, 0, sizeof(strRet)); memset(flagDegree, 0, sizeof(flagDegree)); for (int i = 1; i <= 26; ++i) for (int j = 1; j <= 26; ++j) { if(edge[i][j]) { flagDegree[i] = flagDegree[j] = 1; in_degree[j]++; } } for (int i = 1; i <= 26; ++i) if(flagDegree[i] && !in_degree[i]) s.push(i); int cnt = 0; bool flagCannotDetermined = 0; while(!s.empty()) { if(s.size() > 1) flagCannotDetermined = 1; int temp = s.top(); strRet[cnt++] = 'A'+temp-1; s.pop(); for(int i = 1; i <= 26; ++i) if(edge[temp][i] && (--in_degree[i]) == 0) s.push(i); } strRet[cnt] = '/0'; for(int i = 1; i <= 26; ++i) if(flagDegree[i] && in_degree[i]) return 1; if(flagCannotDetermined) return -1; if(cnt == n) return 0; return -1; } int main() { char str[4]; int i; while (scanf("%d%d", &n, &m) && !(n==0&&m==0)) { memset(edge, 0, sizeof(edge)); bool flagOver = 0, flagCircle = 0, flagNotDetermined = 0; int index; for (i = 1; i <= m; ++i) { cin >> str; edge[str[0]-'A'+1][str[2]-'A'+1] = 1; if(flagCircle || flagNotDetermined || flagOver) continue; int ret = TopoOrder(); if(ret == 0) { flagOver = 1; index = i; } else if(ret == 1) { flagCircle = 1; index = i; } if(i == m && ret == -1) flagNotDetermined = 1; } if(flagCircle) printf("Inconsistency found after %d relations./n", index); else if(flagNotDetermined) printf("Sorted sequence cannot be determined./n"); else printf("Sorted sequence determined after %d relations: %s./n", index, strRet); } return 0; } //这组数据拯救了我,贡献出来 /* 6 8 A<B A<C B<D C<E D<E E<D D<F E<F Right Answer: Inconsistency found after 6 relations. Wrong Answer: Sorted sequence cannot be determined. 原因是: 判断有回路的优先级比判断不可排序的优先级高. 判断不可排序就会返回去录入新的一组值. 我是这样才行的. if(s.size() > 1) flagCannotDetermined = 1; 而不可以直接return -1;//-1代表继续. */