p1712 [NOI2016]区间

传送门

（分析见正睿2018.10.1笔记）

代码

#include<iostream>
#include<cstdio>
#include<cstring>
#include<string>
#include<algorithm>
#include<cctype>
#include<cmath>
#include<cstdlib>
#include<queue>
#include<ctime>
#include<vector>
#include<set>
#include<map>
#include<stack>
using namespace std;
const int inf = 2e9+7;
int d[4001000],col[4001000],n,m,b[1000100],b2[500100],sum,sum2,cnt,S;
int back2[500100];
map<int,int>id,id2;
struct node{
      int x,y,len;
};
node a[500100];
inline int ra(){
      int x=0;char s=getchar();
      while(!isdigit(s))s=getchar();
      while(isdigit(s))x=(x<<3)+(x<<1)+(s-'0'),s=getchar();
      return x;
}
inline bool cmp(const node p,const node q){
      return p.len<q.len;
}
inline void update(int le,int ri,int wh,int x,int y,int k){
      if(le>=x&&ri<=y){
        d[wh]+=k;
        col[wh]+=k;
        return;
      }
      int mid=(le+ri)>>1;
      col[wh<<1]+=col[wh];
      col[wh<<1|1]+=col[wh];
      d[wh<<1]+=col[wh];
      d[wh<<1|1]+=col[wh];
      col[wh]=0;
      if(mid>=x)update(le,mid,wh<<1,x,y,k);
      if(mid<y)update(mid+1,ri,wh<<1|1,x,y,k);
      d[wh]=max(d[wh<<1],d[wh<<1|1]);
      return;
}
int main(){
      register int i,j,k,t;
      int Ans=inf;
      n=ra(),m=ra();
      for(i=1;i<=n;++i){
          a[i].x=ra(),a[i].y=ra();
        if(a[i].x>a[i].y)swap(a[i].x,a[i].y);
        a[i].len=a[i].y-a[i].x;
        b[++cnt]=a[i].x;
        b[++cnt]=a[i].y;
        b2[++S]=a[i].y-a[i].x;
      }
      sort(b+1,b+cnt+1);
      sort(b2+1,b2+S+1); 
      for(i=1;i<=cnt;++i)
        if(!id[b[i]])id[b[i]]=++sum;
      for(i=1;i<=S;++i)
        if(!id2[b2[i]])id2[b2[i]]=++sum2,back2[sum2]=b2[i];
      for(i=1;i<=n;i++){
          a[i].len=id2[a[i].len];
          a[i].x=id[a[i].x];
          a[i].y=id[a[i].y];
      }
      sort(a+1,a+n+1,cmp);
      j=0;k=1;t=1;
      for(k;k<=n;++k)
        if(a[k].len<=1){
          update(1,sum,1,a[k].x,a[k].y,1);
          }else break;
      for(i=1;i<=sum2;++i){
          while(j<sum2&&d[1]<m){
            j++;
            for(k;k<=n;++k)
              if(a[k].len<=j){
                update(1,sum,1,a[k].x,a[k].y,1);
              }else break;
          }
          if(d[1]>=m)Ans=min(Ans,back2[j]-back2[i]);
            else break;
          if(i!=n) 
            for(t;t<=n;++t)
              if(a[t].len<=i){
                update(1,sum,1,a[t].x,a[t].y,-1);
              }else break;
      }
      if(Ans==inf)Ans=-1;
      printf("%d\n",Ans);
      return 0;
}