zoj Grouping(强连通＋缩点＋关键路径)

  1 //First Edit Time:    2014-11-25 13:38
  2 //Last Edit Time:    2014-11-25 14:24
  3 #include<cstdio>
  4 #include<cstring>
  5 #include<vector>
  6 using namespace std;
  7 
  8 #define _clr(x, y) memset(x, y, sizeof (x))
  9 #define Min(x, y) (x < y ? x : y)
 10 #define Max(x, y) (x > y ? x : y)
 11 #define INF 0x3f3f3f3f
 12 #define N  100010
 13 
 14 vector<int> map[N], new_map[N];
 15 int low[N], dfn[N];
 16 int Stack[N], be[N];
 17 bool instack[N];
 18 int dist[N], sum[N];
 19 int top, n, cnt, time;
 20 
 21 void Init()
 22 {
 23     top = time = cnt = 0;
 24     _clr(instack, 0);
 25     _clr(Stack, 0);
 26     _clr(dist, -1);
 27     _clr(low, 0);
 28     _clr(sum, 0);
 29     _clr(dfn, 0);
 30     _clr(be, 0);
 31     for(int i=0; i<=n; i++)
 32     {
 33         map[i].clear();
 34         new_map[i].clear();
 35     }
 36 }
 37 
 38 //ｄｆｓ生成树求强连通分量
 39 void dfs(int u)
 40 {
 41     dfn[u] = low[u] = ++time;
 42     Stack[top++] = u;
 43     instack[u] = true;
 44     for(int i=0; i<(int)map[u].size(); i++)
 45     {
 46         int v = map[u][i];
 47         if(!dfn[v])
 48         {
 49             dfs(v);
 50             low[u] = Min(low[u], low[v]);
 51         }
 52         else if(instack[v])
 53             low[u] = Min(low[u], dfn[v]);
 54     }
 55     if(dfn[u]==low[u])
 56     {
 57         cnt++;
 58         do
 59         {
 60             u = Stack[--top];
 61             instack[u] = false;
 62             be[u] = cnt;
 63             sum[cnt]++;
 64         }while(dfn[u] != low[u]);
 65     }
 66 }
 67 
 68 void Tarjan_Scc()
 69 {
 70     for(int i=1; i<=n; i++)
 71     {
 72         if(!dfn[i])
 73             dfs(i);
 74     }
 75     for(int i=1; i<=n; i++)
 76     {
 77         for(int j=0; j<(int)map[i].size(); j++)
 78         {
 79             int v = map[i][j];
 80             if(be[i] != be[v])
 81                 new_map[be[i]].push_back(be[v]);
 82         }
 83     }
 84 }
 85 
 86 int Get(int u)
 87 {
 88     if(dist[u]!=-1) return dist[u];
 89     dist[u] = 0;
 90     for(int i=0; i<(int)new_map[u].size(); i++)
 91         dist[u] = Max(Get(new_map[u][i]), dist[u]);
 92     return dist[u] = dist[u] + sum[u];
 93 }
 94 
 95 int main()
 96 {
 97     int m, x, y;
 98     while(~scanf("%d%d",&n,&m))
 99     {
100         Init();
101         for(int i=0; i<m; i++)
102         {
103             scanf("%d%d",&x, &y);
104             map[x].push_back(y);
105         }
106 
107         Tarjan_Scc();       //Tarjan算法求强连通缩点为一个ＤＡＧ
108 
109         int ans = -INF;
110         for(int i=1; i<=cnt; i++)   //记忆化搜索求ＤＡＧ关键路径
111            ans = Max(Get(i), ans);
112 
113         printf("%d\n", ans);
114     }
115     return 0;
116 }