hdu 3342 Legal or Not - 拓扑排序
Posted 阿波罗2003
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We all know a master can have many prentices and a prentice may have a lot of masters too, it‘s legal. Nevertheless,some cows are not so honest, they hold illegal relationship. Take HH and 3xian for instant, HH is 3xian‘s master and, at the same time, 3xian is HH‘s master,which is quite illegal! To avoid this,please help us to judge whether their relationship is legal or not.
Please note that the "master and prentice" relation is transitive. It means that if A is B‘s master ans B is C‘s master, then A is C‘s master.
Input
The input consists of several test cases. For each case, the first line contains two integers, N (members to be tested) and M (relationships to be tested)(2 <= N, M <= 100). Then M lines follow, each contains a pair of (x, y) which means x is y‘s master and y is x‘s prentice. The input is terminated by N = 0.
TO MAKE IT SIMPLE, we give every one a number (0, 1, 2,..., N-1). We use their numbers instead of their names.
Output
For each test case, print in one line the judgement of the messy relationship.
If it is legal, output "YES", otherwise "NO".
Sample Input
3 2 0 1 1 2 2 2 0 1 1 0 0 0
Sample Output
YES NO
prentice向master连一条边,然后跑拓扑排序,跑完判一下是否所有点都进过队了。
Code
1 /** 2 * hdu 3 * Problem#3342 4 * Accepted 5 * Time:31ms 6 * Memory:1820k 7 */ 8 #include <iostream> 9 #include <cstdio> 10 #include <ctime> 11 #include <cmath> 12 #include <cctype> 13 #include <cstring> 14 #include <cstdlib> 15 #include <fstream> 16 #include <sstream> 17 #include <algorithm> 18 #include <map> 19 #include <set> 20 #include <stack> 21 #include <queue> 22 #include <vector> 23 #include <stack> 24 #ifndef WIN32 25 #define Auto "%lld" 26 #else 27 #define Auto "%I64d" 28 #endif 29 using namespace std; 30 typedef bool boolean; 31 const signed int inf = (signed)((1u << 31) - 1); 32 const double eps = 1e-6; 33 const int binary_limit = 128; 34 #define smin(a, b) a = min(a, b) 35 #define smax(a, b) a = max(a, b) 36 #define max3(a, b, c) max(a, max(b, c)) 37 #define min3(a, b, c) min(a, min(b, c)) 38 template<typename T> 39 inline boolean readInteger(T& u){ 40 char x; 41 int aFlag = 1; 42 while(!isdigit((x = getchar())) && x != ‘-‘ && x != -1); 43 if(x == -1) { 44 ungetc(x, stdin); 45 return false; 46 } 47 if(x == ‘-‘){ 48 x = getchar(); 49 aFlag = -1; 50 } 51 for(u = x - ‘0‘; isdigit((x = getchar())); u = (u << 1) + (u << 3) + x - ‘0‘); 52 ungetc(x, stdin); 53 u *= aFlag; 54 return true; 55 } 56 57 ///map template starts 58 typedef class Edge{ 59 public: 60 int end; 61 int next; 62 Edge(const int end = 0, const int next = 0):end(end), next(next){} 63 }Edge; 64 65 typedef class MapManager{ 66 public: 67 int ce; 68 int *h; 69 Edge *edge; 70 MapManager(){} 71 MapManager(int points, int limit):ce(0){ 72 h = new int[(const int)(points + 1)]; 73 edge = new Edge[(const int)(limit + 1)]; 74 memset(h, 0, sizeof(int) * (points + 1)); 75 } 76 inline void addEdge(int from, int end){ 77 edge[++ce] = Edge(end, h[from]); 78 h[from] = ce; 79 } 80 inline void addDoubleEdge(int from, int end){ 81 addEdge(from, end); 82 addEdge(end, from); 83 } 84 Edge& operator [] (int pos) { 85 return edge[pos]; 86 } 87 inline void clear() { 88 delete[] edge; 89 delete[] h; 90 } 91 }MapManager; 92 #define m_begin(g, i) (g).h[(i)] 93 ///map template ends 94 95 int n, m; 96 MapManager g; 97 int* dag; 98 99 inline boolean init() { 100 readInteger(n); 101 if(n == 0) return false; 102 readInteger(m); 103 g = MapManager(n, m); 104 dag = new int[(n + 1)]; 105 memset(dag, 0, sizeof(int) * (n + 1)); 106 for(int i = 1, a, b; i <= m; i++) { 107 readInteger(a); 108 readInteger(b); 109 g.addEdge(b, a); 110 dag[a]++; 111 } 112 return true; 113 } 114 115 queue<int> que; 116 inline void topu() { 117 for(int i = 0; i < n; i++) 118 if(!dag[i]) 119 que.push(i); 120 while(!que.empty()) { 121 int e = que.front(); 122 que.pop(); 123 for(int i = m_begin(g, e); i; i = g[i].next) { 124 int& eu = g[i].end; 125 dag[eu]--; 126 if(!dag[eu]) 127 que.push(eu); 128 } 129 } 130 } 131 132 inline void solve() { 133 topu(); 134 for(int i = 0; i < n; i++) { 135 if(dag[i]) { 136 puts("NO"); 137 return; 138 } 139 } 140 puts("YES"); 141 } 142 143 inline void clear() { 144 g.clear(); 145 delete[] dag; 146 } 147 148 int main() { 149 while(init()) { 150 solve(); 151 clear(); 152 } 153 return 0; 154 }
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