[二分答案] P2920 Time Management

推导贪心条件

排序

二分

输出

//#pragma GCC optimize(2)
#include <cstdio>
#include <iostream>
#include <cstdlib>
#include <cmath>
#include <cctype>
#include <string>
#include <cstring>
#include <algorithm>
#include <stack>
#include <queue>
#include <set>
#include <map>
#include <ctime>
#include <vector>
#include <fstream>
#include <list>
#include <iomanip>
#include <numeric>
using namespace std;
typedef long long ll;

const int MAXN = 1e6 + 10;

pair <ll, ll> arr[MAXN];

int N;

bool cmp(pair <ll, ll> a, pair <ll, ll> b)
{
    return a.second < b.second;
}

bool judge(int x)
{
    ll sum = x;

    for(int i = 0; i < N; i++)
    {
        sum += arr[i].first;

        if(sum > arr[i].second)
            return false;
    }

    return true;

}

void bsearch()
{
    int fst = 0, lst = MAXN, mid, ans;
    

    if(!judge(0))
    {
        cout<<"-1"<<endl;
        return ;
    }

    while(fst <= lst)
    {
        mid = (fst + lst) / 2;

        if(judge(mid))
        {
            ans = mid;
            fst = mid + 1;
        }
        else
            lst = mid - 1;
    }

    cout<<ans<<endl;

}


int main()
{
    //ios::sync_with_stdio(false);

    //cin.tie(0);     cout.tie(0);

    cin>>N;

    for(int i = 0; i < N; i++)
        cin>>arr[i].first>>arr[i].second;

    sort(arr, arr + N, cmp);

    bsearch();

    return 0;
}