(easy version)

https://codeforces.com/contest/1165/problem/F1

(hard version)

https://codeforces.com/contest/1165/problem/F2

题意：每天可以取得一块钱，每件物品平时价格是2块钱，活动价格是1块钱，给你每件物品需要的件数，和每天活动的商品，求最小几天可以买齐？

题解：二分

/*
*@Author:   STZG
*@Language: C++
*/
#include <bits/stdc++.h>
#include<iostream>
#include<algorithm>
#include<cstdlib>
#include<cstring>
#include<cstdio>
#include<string>
#include<vector>
#include<bitset>
#include<queue>
#include<deque>
#include<stack>
#include<cmath>
#include<list>
#include<map>
#include<set>
//#define DEBUG
#define RI register int
#define endl "\n"
using namespace std;
typedef long long ll;
//typedef __int128 lll;
const int N=200000+10;
const int M=100000+10;
const int MOD=1e9+7;
const double PI = acos(-1.0);
const double EXP = 1E-8;
const int INF = 0x3f3f3f3f;
int t,n,m,k,p,l,r,d;
int ans,cnt,flag,temp,sum;
int a[N],b[N];
char str;
struct node{};
vector<int>v[N<<1];
bool sloved(int mid){
    sum=0;
    temp=cnt;
    for(int i=1;i<=n;i++)b[i]=a[i];
    for(int i=mid;i>=1;i--){
        for(int j=0;j<v[i].size();j++){
            while(b[v[i][j]]&&mid){
                mid--;
                temp--;
                b[v[i][j]]--;
            }
        }
        if(mid>=i)mid--,sum++;
    }
    return sum/2>=temp;
}
int main()
{
#ifdef DEBUG
	freopen("input.in", "r", stdin);
	//freopen("output.out", "w", stdout);
#endif
    //ios::sync_with_stdio(false);
    //cin.tie(0);
    //cout.tie(0);
    //scanf("%d",&t);
    //while(t--){
    scanf("%d%d",&n,&m);
    for(int i=1;i<=n;i++)scanf("%d",&a[i]),cnt+=a[i];
    for(int i=1;i<=m;i++){
        scanf("%d%d",&d,&t);
        v[d].push_back(t);
    }
    l=cnt;
    r=2*cnt;
    while(l<=r){
        int mid=(l+r)>>1;
        if(sloved(mid)){
            ans=mid;
            r=mid-1;
        }else{
            l=mid+1;
        }
    }
    cout<<ans<<endl;
    //}

#ifdef DEBUG
	printf("Time cost : %lf s\n",(double)clock()/CLOCKS_PER_SEC);
#endif
    //cout << "Hello world!" << endl;
    return 0;
}