HDU3887 DFS序+ 线段树

查询树上某个节点的子节点的标号小于其标号的数目. 一个trick是建立线段树之后,从标号小的向标号大的来做更新.

   1:  #include <cstdio>

   2:  #include <cstring>

   3:  #include <cctype>

   4:  #include <algorithm>

   5:  #include <vector>

   6:  #include <iostream>

   7:  using namespace std;

   8:  #pragma comment(linker, "/STACK:1024000000,1024000000")

   9:  #define LL(a)   a<<1

  10:  #define RR(a)   a<<1|1

  11:   

  12:  const int MaxL = 200030;

  13:   

  14:  int pre[MaxL];  // first travel

  15:  int nxt[MaxL];  // nxt travel

  16:  int f[MaxL];

  17:  bool vis[MaxL];

  18:  int N;

  19:  vector<vector<int> > E(MaxL);

  20:   

  21:  struct Seg_tree

  22:  {

  23:      int left, right;

  24:      int sum;

  25:  } tt[MaxL<<2];

  26:   

  27:   

  28:  void PushUp(int idx)

  29:  {

  30:      tt[idx].sum = tt[LL(idx)].sum + tt[RR(idx)].sum;

  31:  }

  32:   

  33:  void build(int l,int r,int idx)

  34:  {

  35:      tt[idx].left = l, tt[idx].right = r;

  36:      tt[idx].sum = 0;

  37:      if (l == r) return ;

  38:      int m = (l + r) >> 1;

  39:      build(l,m, LL(idx));

  40:      build(m+1, r, RR(idx));

  41:  }

  42:   

  43:  void update(int p, int idx = 1)

  44:  {

  45:      if(p == tt[idx].left && p == tt[idx].right)

  46:      {

  47:          tt[idx].sum =1;

  48:          return ;

  49:      }

  50:      int mid = (tt[idx].left + tt[idx].right)>>1;

  51:      if(p <= mid) update(p, LL(idx));

  52:      else update(p, RR(idx));

  53:      PushUp(idx);

  54:  }

  55:   

  56:  int query(int l, int r, int idx = 1)

  57:  {

  58:      if(l == tt[idx].left && r ==tt[idx].right)

  59:          return tt[idx].sum;

  60:      int mid = (tt[idx].left + tt[idx].right)>>1;

  61:      if(r <= mid) return query(l,r, LL(idx));

  62:      else if(l> mid) return query(l,r, RR(idx));

  63:      else

  64:          return query(l, mid, LL(idx))+ query(mid+1, r, RR(idx));

  65:  }

  66:   

  67:  int mark = 1;

  68:  void dfs( int a)

  69:  {

  70:      vis[a] = 1;

  71:      pre[a] = mark++;

  72:      for(int i=0; i<E[a].size(); i++)

  73:      {

  74:          if(!vis[E[a][i]])

  75:              dfs(E[a][i]);

  76:      }

  77:      nxt[a] = mark++;

  78:  }

  79:   

  80:  int main()

  81:  {

  82:  //    freopen("1.txt","r",stdin);

  83:      int p;

  84:      while( scanf("%d%d", &N, &p) && N!=0 && p!=0)

  85:      {

  86:          memset(pre, 0, sizeof(pre));

  87:          memset(nxt, 0 ,sizeof(nxt));

  88:          memset(vis, 0 ,sizeof(vis));

  89:          for(int i=1; i<=N; i++) E[i].clear();

  90:   

  91:          for(int i=1; i<N; i++)

  92:          {

  93:              int a,b;

  94:              scanf("%d%d", &a,&b);

  95:              E[a].push_back(b);

  96:              E[b].push_back(a);

  97:          }

  98:          mark = 1;

  99:          dfs(p);

 100:          build(1, 2*N, 1);

 101:          for(int i=1; i<=N; i++)

 102:          {

 103:              f[i] =query(pre[i], nxt[i],1);

 104:              update(pre[i],1);

 105:          }

 106:          for(int i=1; i<N; i++)

 107:              printf("%d ",f[i]);

 108:          printf("%d\n",f[N]);

 109:      }

 110:      return 0;

 111:  }

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