Salary Changing CF-1251D（二分）

题意：

有$n$个员工，$s$元钱，现在要给每个员工发工资。每个员工的工资的范围$(l_i,r_i)$，求所有员工的工资中位数的最大值。

思路：

二分答案，$check$的时候判断工资可以大于等于$mid$的员工个数，用最小代价购买之后判断总价钱会不会超出范围。

代码：

//#include<bits/stdc++.h>
#include <set>
#include <map>
#include <stack>
#include <cmath>
#include <queue>
#include <cstdio>
#include <string>
#include <vector>
#include <cstring>
#include <iostream>
#include <algorithm>

#define ll long long
#define pll pair<ll,ll>
#define pii pair<int,int>
#define bug printf("*********
")
#define FIN freopen("input.txt","r",stdin);
#define FON freopen("output.txt","w+",stdout);
#define IO ios::sync_with_stdio(false),cin.tie(0)
#define ls root<<1
#define rs root<<1|1
#define pb push_back

using namespace std;
const int inf = 2e9 + 7;
const ll Inf = 1e18 + 7;
const int maxn = 2e5 + 5;
const int mod = 1e9 + 7;

struct node
{
    ll l, r;
}p[maxn];

ll s, n;

bool cmp(const node& a, const node& b)
{
    return a.l < b.l;
}

bool check(ll x)
{
    ll res = 0, m = (n + 1) >> 1;
    for (int i = n; i >= 1; --i)
    {
        if (m && p[i].l <= x && p[i].r >= x)
        {
            res += x;
            m--;
        }
        else
        {
            res += p[i].l;
            if (p[i].l >= x && m)    m--;
        }
    }
    if (m || res > s)    return 0;
    return 1;
}


int main()
{
    int T;
    scanf("%d", &T);
    while (T--)
    {
        scanf("%lld %lld", &n, &s);
        for (int i = 1; i <= n; ++i)
        {
            scanf("%lld %lld", &p[i].l, &p[i].r);
        }
        sort(p + 1, p + 1 + n, cmp);
        ll l = 0, r = s;
        while (l <= r)
        {
            ll mid = (l + r) >> 1;
            if (check(mid))    l = mid + 1;
            else r = mid - 1;
        }
        printf("%lld
", l - 1);
    }
}