D - Mayor's posters（离散化）

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

#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
using namespace std;
const int maxn=100010;
int n;
struct edge{
   
    int l;
    int r;
}e[maxn<<2];
int ans;
struct node{
   
    int l;
    int r;
    int laz;
    int val;
}tree[maxn<<2];
int vis[maxn<<2];
int pos[maxn][2],a[maxn<<2];
int casen;
void build(int l,int r,int cur){
   
    tree[cur].l=l;
    tree[cur].r=r;
    tree[cur].val=0;
    if(l==r)
        return;
    int mid=(l+r)/2;
    build(l,mid,cur<<1);
    build(mid+1,r,cur<<1|1);
}
void pushdown(int cur){
   
    if(tree[cur].val!=0){
   	
        tree[cur<<1].val=tree[cur<<1|1].val=tree[cur].val;
        tree[cur].val=0;
    }
    return;
}
void update(int pl,int pr,int cur,int color)
{
   
    if(pl<=tree[cur].l&&tree[cur].r<=pr){
   
        tree[cur].val=color;
        return;
    }
    pushdown(cur);
    int mid=(tree[cur].l+tree[cur].r)/2;
    if(pl<=mid)
        update(pl,pr,cur<<1,color);
    if(pr>mid)
        update(pl,pr,cur<<1|1,color);
}
void query(int cur){
   
    if(tree[cur].val!=0){
   	
        if(!vis[tree[cur].val]){
   
            vis[tree[cur].val]=1;
            ans++;
        }
        return;
    }
    query(cur<<1);
    query(cur<<1|1);
}
int main(){
   
    cin>>casen;
    while(casen--){
   
        memset(vis,0,sizeof(vis));
        memset(a,0,sizeof(a));
        memset(pos,0,sizeof(pos));
        scanf("%d",&n);
        int id=0;
        for(int i=1;i<=n;i++){
   
              scanf("%d%d",&pos[i][0],&pos[i][1]);
              a[++id]=pos[i][0];
              a[++id]=pos[i][1];
        }
        sort(a+1,a+id+1);
        int cnt=1;
        for(int i=2;i<=id;i++){
   
            if(a[i]!=a[i-1]){
   
                a[++cnt]=a[i];
            }
        }
        ans=0;
        int R=0;
        for(int i=1;i<=n;i++){
   
            int ul=lower_bound(a+1,a+1+cnt,pos[i][0])-a;
            int ur=lower_bound(a+1,a+1+cnt,pos[i][1])-a;
            e[i].l=ul;
            e[i].r=ur;
            R=max(R,e[i].r);
        }
        build(1,R,1);
        for(int i=1;i<=n;i++){
   
            update(e[i].l,e[i].r,1,i);
        }
        query(1);
        printf("%d\n",ans);
    }
return 0;
}