洛谷P1083借教室 （二分答案）

https://www.luogu.com.cn/problem/P1083

ac代码:

#include<iostream>
#include<cstring>
using namespace std;
const int maxn=1e6+5;

int n,m;
int room[maxn],d[maxn],l[maxn],r[maxn],a[maxn],need[maxn];
bool check(int x){
    memset(a,0,sizeof(a));
    for(int i=1;i<=x;i++){
        a[l[i]]+=d[i];
        a[r[i]+1]-=d[i];
    }
    for(int i=1;i<=n;i++){
        need[i]=need[i-1]+a[i];//差分思想
        if(need[i]>room[i]) return 0;
    }
    return 1;
}
int main(){
    cin>>n>>m;
    for(int i=1;i<=n;i++) cin>>room[i];
    for(int i=1;i<=m;i++){
        cin>>d[i]>>l[i]>>r[i];
    }
    if(check(m)){cout<<"0";return 0;}
    int left=1,right=m;
    while(left<right){
        int mid=(left+right)/2;
        if(check(mid))
            left=mid+1;
        else
            right=mid;//mid可能是答案，所以right=mid而不是mid-1;
    }
    cout<<"-1"<<endl<<left;
    return 0;
}