[NOIP2012]借教室（二分）

 

你咯的定级真是雾……二分入门水题

前缀和维护一下借的天数，二分查找答案，就酱~！

#include<bits/stdc++.h>
using namespace std;
const int N = 1000050;
int n,m;
long long r[N],d[N],a[N];
int s[N],t[N];
bool check(int mid)
{
    memset(a,0,sizeof(a));
    for(int i = 1; i <= mid; i++){
        //前缀和记录要借的 
        a[s[i]] += d[i];
        a[t[i] + 1] -= d[i];
    }
    for(int i = 1; i <= n; i++){
        a[i] += a[i-1];  //前缀和处理完毕~?ヽ(°▽°)ノ? 
        if(a[i] > r[i])return 0;
    } 
    return 1;
}
signed main()
{
   cin>>n>>m;
   for(int i = 1; i <= n; i++ )cin>>r[i];
   for(int i = 1; i <= m; i++ )scanf("%d%d%d",&d[i],&s[i],&t[i]);
   if(check(m))printf("0");   
   else {
       int l = 1,r = m;
       while(l < r){
        int mid = l + (r - l) / 2;
        if(check(mid)){
             l = mid + 1;  //根据mid定义可知  此时前段都能借到，那就向后查找
        }
        else r = mid;
    }printf("-1\n%d",l);
   }
}