CCF 202012-1-期末预测之最佳阈值

# include <bits/stdc++.h>
# define MAX (100000+10) 
//# define DB
# define pt puts("")

using namespace std;

struct node{
    int a, b;    
    
    node(int x, int y):a(x),b(y){}
    node(){}
    
    friend bool operator <(const node x, const node y){
        return x.a < y.a;
    }
    friend bool operator <=(const node x, const node y){
        return x.a <= y.a;
    }
    friend bool operator >(const node x, const node y){
        return x.a > y.a;
    }
};

vector<node> ve;

map<int, int> mp;
vector<int> xita;

int preSum[MAX];

int main(){
    ios::sync_with_stdio(false);
    
    int n;
    cin>>n;
    node now;
    
    for(int i=0;i<n;++i){

        cin>>now.a>>now.b;
        ve.push_back(now);
        
        if(!mp.count(now.a)){
            mp[now.a] = 1;
            xita.push_back(now.a);
        }
        
    }
    
    sort(xita.begin(), xita.end() );
    sort(ve.begin(), ve.end() );
    
    preSum[0] = ve[0].b;
    for(int i=1; i<n; ++i){
        preSum[i] = preSum[i-1] + ve[i].b;
    }
    
    int len = xita.size();
    int j=0;
    int max=-1, rec;
    
#ifdef DB
    for(int i=0; i<ve.size(); ++i){
        cout << "ve[i].a=" << ve[i].a <<"  ve[i].b=" << ve[i].b <<endl;
    }
        
    for(int i=0; i<xita.size(); ++i){
        cout << xita[i] << " ";
    } 
    pt;
#endif

    for(int i=0; i<len; ++i){// get temp xita, xita[i]
        
        while(ve[j].a < xita[i] && j < n-1) j++;
//        cout << "j=" << j << endl;
        int zero = 0, one = preSum[n-1];
        if(j > 0){
            zero = (j - preSum[j - 1]);
            one = preSum[n-1] - preSum[j-1];
        }
            
        int ans = one + zero;
//        cout << "zero="<<zero<<" one="<<one<<" ans="<<ans<<endl;
    
        if(ans > max){
            max = ans;
            rec = xita[i];
        }else if(ans == max){
            if(xita[i] > rec) rec = xita[i];
        }
        
//        cout << "ans = " << ans << endl;

    }
    
    cout << rec << endl;
    return 0;
}