POJ-2528-Mayor's posters（线段树+离散化）

The citizens of Bytetown, AB, could not stand that the candidates in the mayoral election campaign have been placing their electoral posters at all places at their whim. The city council has finally decided to build an electoral wall for placing the posters and introduce the following rules: 
  • Every candidate can place exactly one poster on the wall. 
  • All posters are of the same height equal to the height of the wall; the width of a poster can be any integer number of bytes (byte is the unit of length in Bytetown). 
  • The wall is divided into segments and the width of each segment is one byte. 
  • Each poster must completely cover a contiguous number of wall segments.

They have built a wall 10000000 bytes long (such that there is enough place for all candidates). When the electoral campaign was restarted, the candidates were placing their posters on the wall and their posters differed widely in width. Moreover, the candidates started placing their posters on wall segments already occupied by other posters. Everyone in Bytetown was curious whose posters will be visible (entirely or in part) on the last day before elections. 
Your task is to find the number of visible posters when all the posters are placed given the information about posters' size, their place and order of placement on the electoral wall. 

Input

The first line of input contains a number c giving the number of cases that follow. The first line of data for a single case contains number 1 <= n <= 10000. The subsequent n lines describe the posters in the order in which they were placed. The i-th line among the n lines contains two integer numbers l i and ri which are the number of the wall segment occupied by the left end and the right end of the i-th poster, respectively. We know that for each 1 <= i <= n, 1 <= l i <= ri <= 10000000. After the i-th poster is placed, it entirely covers all wall segments numbered l i, l i+1 ,... , ri.

Output

For each input data set print the number of visible posters after all the posters are placed. 

The picture below illustrates the case of the sample input. 

Sample Input

1
5
1 4
2 6
8 10
3 4
7 10

Sample Output

4

题解

这道题老师是放在线段树专题的，很久前做一直没有A，今天想再做做看，发现之前我有一个数组没有清零之前还没有查出来。

这道题给你墙的长度有10000000，如果直接线段树上的话肯定是不行，我们看到n才10000，所以我们可以离散化一下，这样只有20000的长度了

每次区间的时候就用lazy tag就可以了

最后统计有多少种海报数的时候我们可以dfs搜一下

不是叶子结点就下放标记

当搜到叶子节点的时候我们判断一下这种海报出现过没有就可以了

 1 #include<algorithm>
 2 #include<cstdio>
 3 #include<cstring>
 4 #include<cmath>
 5 #define N 10005
 6 #define maxn 20000
 7 using namespace std;
 8 int T,n,cnt,num,ans;
 9 int l[N],r[N];
10 bool t[maxn];
11 int mark[4*maxn];
12 struct node{
13     int num,id,p;
14 }a[2*N];
15 bool cmp(node x,node y){
16     if (x.num!=y.num) return x.num<y.num;
17                 else return x.id<y.id;
18 }
19 void change(int v,int l,int r,int x,int y,int k){
20     if (l==x&&r==y){
21         mark[v]=k;
22         return;
23     }
24     if (mark[v]>0){
25         mark[v<<1]=mark[v];
26         mark[1+(v<<1)]=mark[v];
27         mark[v]=0;
28     }
29     int mid=(l+r)>>1;
30     if (mid>=y) change(v<<1,l,mid,x,y,k); else
31     if (x>mid) change(1+(v<<1),mid+1,r,x,y,k); else{
32         change(v<<1,l,mid,x,mid,k);
33         change(1+(v<<1),mid+1,r,mid+1,y,k);
34     }
35 }
36 void find(int v,int l,int r){
37     int mid=(l+r)>>1;
38     if (l==r){
39         if (!t[mark[v]]){
40             t[mark[v]]=true;
41             ans++;
42         }
43         return;
44     }
45     if (mark[v]>0){
46         mark[v<<1]=mark[v];
47         mark[1+(v<<1)]=mark[v];
48         mark[v]=0;
49     }
50     find(v<<1,l,mid);
51     find(1+(v<<1),mid+1,r);
52 }
53 int main(){
54     scanf("%d",&T);
55     while (T--){
56         memset(mark,0,sizeof(mark));
57         memset(t,0,sizeof(t));
58         cnt=0;
59         scanf("%d",&n);
60         for (int i=1;i<=n;i++){
61             scanf("%d%d",&l[i],&r[i]);
62             a[++cnt].num=l[i]; a[cnt].id=i; a[cnt].p=cnt;
63             a[++cnt].num=r[i]; a[cnt].id=i; a[cnt].p=cnt;
64         }
65         sort(a+1,a+1+cnt,cmp);
66         int s;
67         num=1;
68         for (int i=2;i<=cnt;i++){
69             s=a[i-1].id;
70             if (a[i-1].p%2) l[s]=num;
71                         else r[s]=num;
72             if (a[i].num!=a[i-1].num) num++;
73         } 
74         s=a[cnt].id;
75         if (a[cnt].p%2) l[s]=num;
76                     else r[s]=num;
77         for (int i=1;i<=n;i++)
78             change(1,1,num,l[i],r[i],i);
79         ans=0;
80         find(1,1,num);
81         printf("%d\n",ans);
82     }
83     return 0;
84 }
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posted @ 2017-09-25 16:36  I__am  阅读(160)  评论(0)  编辑  收藏  举报