并查集。
这题错了不少次才过的。
分析见代码。
http://poj.org/problem?id=1703
1 #include <cstdio> 2 #include <cstring> 3 #include <algorithm> 4 using namespace std; 5 const int maxn = 1e5 + 10; 6 const char str1[] = "Not sure yet."; 7 const char str2[] = "In different gangs."; 8 const char str3[] = "In the same gang."; 9 int fa[maxn], belong[maxn], nex[maxn]; 10 int n, m, u, v, k; 11 char op; 12 13 int father(int u){ 14 //WHAT WOULD CAUSE AN INFINITE LOOP 15 if(fa[u] == -1) return u; 16 int tem = father(fa[u]); 17 belong[u] = belong[tem]; 18 fa[u] = tem; 19 return tem; 20 } 21 22 void solve(){ 23 if(op == 'D'){ 24 if(belong[u] == -1 && belong[v] == -1){ 25 //this is the simplest case 26 belong[u] = k++; 27 belong[v] = k++; 28 nex[u] = v; 29 nex[v] = u; 30 return; 31 } 32 if(belong[u] != -1 && belong[v] == -1){ 33 //notice that v is never mentioned, but u is already processed 34 //since is u is vistied, u got its partner 35 int fu = father(u), fu1 = father(nex[u]); 36 //draw a line from v to u1 37 fa[v] = fu1; 38 nex[v] = fu; 39 belong[v] = belong[fu1]; 40 return; 41 //match a virtue partner for node u 42 } 43 if(belong[u] == -1 && belong[v] != -1){ 44 int fv = father(v), fv1 = father(nex[v]); 45 fa[u] = fv1; 46 nex[u] = fv; 47 belong[u] = belong[fv1]; 48 return; 49 } 50 if(belong[u] != -1 && belong[v] != -1){ 51 //notice that both u and v is already visited 52 int fu = father(u), fu1 = father(nex[u]); 53 int fv = father(v), fv1 = father(nex[v]); 54 int bu = belong[fu] >> 1; 55 int bv = belong[fv] >> 1; 56 if(bu > bv){ 57 // v is relatively primitive 58 fa[fu] = fv1; 59 fa[fu1] = fv; 60 return; 61 } 62 if(bu < bv){ 63 fa[fv] = fu1; 64 fa[fv1] = fu; 65 return; 66 } 67 } 68 } 69 if(op == 'A'){ 70 int fu = father(u); 71 int fv = father(v); 72 if(belong[fu] == -1 || belong[fv] == -1) puts(str1); 73 else if(belong[fu] == belong[fv]) puts(str3); 74 else if(belong[fu] == (1 ^ belong[fv])) puts(str2); 75 else puts(str1); 76 } 77 } 78 79 int main(){ 80 freopen("in.txt", "r", stdin); 81 int T; 82 scanf("%d", &T); 83 while(T--){ 84 scanf("%d%d", &n, &m); 85 memset(belong, -1, sizeof belong); 86 memset(fa, -1, sizeof fa); 87 k = 0; 88 for(int i = 0; i < m; i++){ 89 scanf(" %c%d%d", &op, &u, &v); 90 solve(); 91 } 92 } 93 }