【二分】NOIP2011聪明的质检员

#include<iostream>
#include<stdio.h>
#include<algorithm>
#include<cmath>
#include<iomanip>
using namespace std;
void preprocess(int weight);
struct Node{
int l,r;
};
const int SIZE=200005;
Node node[SIZE];
int n,counter[SIZE],wei[SIZE],value[SIZE];
double total[SIZE];

int main(){
double interval,min_dis,tmp;
double standard;
int left,right;

cin>>n>>interval>>standard;
double sum=0;
int maximum=-1;
for(int i=1;i<=n;i++){
scanf("%d%d",&wei[i],&value[i]);
maximum=max(wei[i],maximum);
sum+=value[i];
}
min_dis=sum*n;
for(int i=1;i<=interval;i++){
scanf("%d%d",&node[i].l,&node[i].r);
//node[i].l--;  node[i].r--;
}
left=0; right=maximum;

//进行二分查找
while(left<=right){
//cout<<"left: "<<left<<" right: "<<right<<endl;
int middle=(left+right)/2;
//动态规划，O(n)的时间完成预处理
preprocess(middle);
tmp=0;
for(int i=1;i<=interval;i++){
tmp+=(counter[node[i].r]-counter[node[i].l-1])*(total[node[i].r]-total[node[i].l-1]);
}
//所选的重量越大，检验量就会越大，毫无意义
if(tmp>standard)
left=middle+1;
else if(tmp<standard)
right=middle-1;
else if(tmp==standard){
min_dis=standard;
break;
}
if(fabs(tmp-standard)<fabs(min_dis-standard))
min_dis=tmp;
//if((tmp>=standard&&tmp<min_dis)||(tmp<standard&&tmp>min_dis))
//	min_dis=tmp;
//cout<<"middle: "<<middle<<" min_dis "<<min_dis<<endl;
}

if(min_dis>standard)
cout<<fixed<<setprecision(0)<<min_dis-standard<<endl;
else cout<<fixed<<setprecision(0)<<standard-min_dis<<endl;
//system("pause");
return 0;
}

void preprocess(int weight){
counter[0]=0; total[0]=0;
if(wei[1]>=weight){
counter[1]=1;
total[1]=value[1];
}
else{
counter[1]=0;
total[1]=0;
}
for(int i=2;i<=n;i++){
if(wei[i]>=weight){
counter[i]=counter[i-1]+1;
total[i]=total[i-1]+value[i];
}
else{
counter[i]=counter[i-1];
total[i]=total[i-1];
}
}
return;
}