J - Assign the task HDU - DFS序-线段树

• J - Assign the task

•  HDU - 3974 
• 按照dfs序建树，区间更新点查询

• #include<iostream>
  #include<stdio.h>
  #include<cstring>
  using namespace std;
  #define maxn 50020
  struct edg
  {
      int to,v;
  } edge[maxn];
  int head[maxn],tot,t;
  int cnt,start[maxn];
  int n,END[maxn],u,v;
  bool vis[maxn];
  struct node
  {
      int l,r,val,lazy;
  } tree[maxn*4];
  void init()
  {
      tot=cnt=0;
      memset(head,-1,sizeof(head));
      memset(vis,0,sizeof(vis));
  }
  void addedge(int u,int v)
  {
      edge[++tot].v=v;
      edge[tot].to=head[u];
      head[u]=tot;
  }
  void dfs(int u)
  {
      ++cnt;
      start[u]=cnt;
      for(int i=head[u]; i!=-1; i=edge[i].to)
          dfs(edge[i].v);
      END[u]=cnt;
  }
  void push_up(int root,int v)
  {
      tree[root].val=v;
      tree[root].lazy=1;
  }
  void push_down(int root)
  {
      if(tree[root].lazy)
      {
          push_up(root<<1,tree[root].val);
          push_up(root<<1|1,tree[root].val);
          tree[root].lazy = 0;
      }
  }
  void build(int i,int l,int r)
  {
      tree[i].l = l;
      tree[i].r = r;
      tree[i].val = -1;
      tree[i].lazy = 0;
      if(l == r)return;
      int mid = (l+r)/2;
      build(i<<1,l,mid);
      build((i<<1)|1,mid+1,r);
  }
  void update(int i,int l,int r,int v)
  {
      if(tree[i].l == l && tree[i].r == r)
      {
          push_up(i,v);
          return;
      }
      push_down(i);
      int mid = (tree[i].l + tree[i].r)/2;
      if(r <= mid)update(i<<1,l,r,v);
      else if(l > mid)update((i<<1)|1,l,r,v);
      else
      {
          update(i<<1,l,mid,v);
          update((i<<1)|1,mid+1,r,v);
      }
  }
  int query(int i,int u)
  {
      if(tree[i].l == u && tree[i].r == u)
          return tree[i].val;
      push_down(i);
      int mid = (tree[i].l + tree[i].r)/2;
      if(u <= mid)return query(i<<1,u);
      else return query((i<<1)|1,u);
  }
  int main()
  {
      scanf("%d",&t);
      for(int cas=1; cas<=t; cas++)
      {
          printf("Case #%d:\n",cas);
          init();
          scanf("%d",&n);
          for(int i = 1; i < n; i++)
          {
              scanf("%d%d",&u,&v);
              vis[u] = true;
              addedge(v,u);
          }
          for(int i = 1; i <= n; i++)
              if(!vis[i])
              {
                  dfs(i);
                  break;
              }
          build(1,1,cnt);
          char op[10];
          int m;
          scanf("%d",&m);
          while(m--)
          {
              scanf("%s",op);
              if(op[0] == 'C')
              {
                  scanf("%d",&u);
                  printf("%d\n",query(1,start[u]));
              }
              else
              {
                  scanf("%d%d",&u,&v);
                  update(1,start[u],END[u],v);
              }
          }
      }
      return 0;
  }