codeforces 1251D 二分+贪心

题意：给了n个人，每个人两个属性l，r。表示能拿工资的范围。boss有s元，问最多可以使n人拿到的工资的中位数最大。

思路：分别根据l，r进行两次排序，求出可以二分的区间，然后对于每个中位数，进行二分。ri小于x的人和li大于x的人拿li元（所以在二分前，要排序让li小的在前面），为了让钱更多给其他的人。对于其他人，按照li从小到大排序。

优先补充x左面的人，即sum += li。补充右面的人只需要sum+=x即可。

#include <iostream>
#include <cmath>
#include <cstdio>
#include <cstring>
#include <string>
#include <map>
#include <iomanip>
#include <algorithm>
#include <queue>
#include <stack>
#include <set>
#include <vector> 
// #include <bits/stdc++.h>
#define fastio ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);
#define sp ' '
#define endl '
'
#define inf  0x3f3f3f3f;
#define FOR(i,a,b) for( int i = a;i <= b;++i)
#define bug cout<<"--------------"<<endl
#define P pair<int, int>
#define fi first
#define se second
#define pb(x) push_back(x)
#define ppb() pop_back()
#define mp(a,b) make_pair(a,b)
#define ms(v,x) memset(v,x,sizeof(v))
#define rep(i,a,b) for(int i=a;i<=b;i++)
#define repd(i,a,b) for(int i=a;i>=b;i--)
#define sca3(a,b,c) scanf("%d %d %d",&(a),&(b),&(c))
#define sca2(a,b) scanf("%d %d",&(a),&(b))
#define sca(a) scanf("%d",&(a));
#define sca3ll(a,b,c) scanf("%lld %lld %lld",&(a),&(b),&(c))
#define sca2ll(a,b) scanf("%lld %lld",&(a),&(b))
#define scall(a) scanf("%lld",&(a));


using namespace std;
typedef long long ll;
ll gcd(ll a,ll b){return b?gcd(b,a%b):a;}
ll lcm(ll a,ll b){return a/gcd(a,b)*b;}
ll powmod(ll a, ll b, ll mod){ll sum = 1;while (b) {if (b & 1) {sum = (sum * a) % mod;b--;}b /= 2;a = a * a % mod;}return sum;}

const double Pi = acos(-1.0);
const double epsilon = Pi/180.0;
const int maxn = 2e5+10;
ll n,s;
struct node
{
    ll l,r;
}a[maxn];
bool cmp1(node a,node b)
{
    return a.l > b.l;
}
bool cmp2(node a,node b)
{
    return a.r > b.r;
}
ll judge(int x)
{
    std::vector<int>v;
    ll sum = 0;
    ll cnt1 = 0,cnt2 = 0;
    rep(i,1,n){
        if(a[i].r < x){
            sum += a[i].l;
            cnt1++;
        }
        else if(x < a[i].l){
            sum += a[i].l;
            cnt2++;
        }
        else {
            v.pb(a[i].l);
        }
    }
    sort(v.begin(),v.end());
    for(auto i : v){
        if(cnt1 < n/2){
            sum += i;
            cnt1++;
        }
        else sum += x; 
    }
    if(sum > s) return 0;
    else return 1;

}
int main()
{
    //freopen("input.txt", "r", stdin);
    int _;
    scanf("%d",&_);
    while(_--)
    {
        cin>>n>>s;
        rep(i,1,n) cin>>a[i].l>>a[i].r;
        sort(a+1,a+1+n,cmp1);
        ll L = a[n/2+1].l;
        sort(a+1,a+1+n,cmp2);
        ll R = a[n/2+1].r;
        sort(a+1,a+1+n,cmp1);
        ll ans = 0;
        //L = 1,R = 1e9;
        while(L <= R){
            ll mid = (L+R)/2;
            if(judge(mid)){
                ans = max(mid,ans);
                L = mid+1;
            }
            else R = mid-1;
        }
        cout<<ans<<endl;
    }
}