贪心 HDOJ 5385 The Path

题目传送门

 /*
     题意：给一张图和一些有向边，问如何给边赋值使得d1 < d2 < .. < dx > ,,,< ddn
     贪心：左边从2开始，右边从n开始，每次选择未标记且相连的点加入树，加入时间就是d[i]，若不在树上的输出n，注意重边和重点
 */
 /************************************************
  * Author        :Running_Time
  * Created Time  :2015-8-13 12:09:17
  * File Name     :F.cpp
  ************************************************/

 #include <cstdio>
 #include <algorithm>
 #include <iostream>
 #include <sstream>
 #include <cstring>
 #include <cmath>
 #include <string>
 #include <vector>
 #include <queue>
 #include <deque>
 #include <stack>
 #include <list>
 #include <map>
 #include <set>
 #include <bitset>
 #include <cstdlib>
 #include <ctime>
 using namespace std;

 #define lson l, mid, rt << 1
 #define rson mid + 1, r, rt << 1 | 1
 typedef long long ll;
 const int MAXN = 3e5 + ;
 const int MAXM = 6e5 + ;
 const int INF = 0x3f3f3f3f;
 const int MOD = 1e9 + ;
 vector<int> G[MAXN];
 bool vis[MAXN];
 int fa[MAXN];
 int d[MAXN];
 int u[MAXN], v[MAXN];
 int n, m;

 void mark(int u)    {
     for (int i=; i<G[u].size (); ++i)  {
         int v = G[u][i];
         if (fa[v] || vis[v])  continue;
         fa[v] = u;
     }
 }

 void work(void) {
     memset (d, , sizeof (d));
     memset (fa, , sizeof (fa));
     memset (vis, false, sizeof (vis));
     int l = , r = n, now = ;
     fa[] = ;  vis[] = true;  mark ();
     while (l <= r)  {
         if (fa[l])  {
             mark (l);   vis[l] = true;
             d[l] = ++now;   l++;   continue;
         }
         if (fa[r])  {
             mark (r);   vis[r] = true;
             d[r] = ++now;   r--;
         }
     }

     for (int i=; i<=m; ++i)    {
         if (fa[v[i]] != u[i])   printf ("%d\n", n);
         else    printf ("%d\n", abs (d[u[i]] - d[v[i]]));
     }
 }

 int main(void)    {     //HDOJ 5385 The Path
     int T;  scanf ("%d", &T);
     while (T--) {
         scanf ("%d%d", &n, &m);
         for (int i=; i<=n; ++i)    G[i].clear ();
         for (int i=; i<=m; ++i)    {
             scanf ("%d%d", &u[i], &v[i]);
             G[u[i]].push_back (v[i]);
         }
         work ();
     }

     return ;
 }