为什么这样改可以AC

#include<bits/stdc++.h>
using namespace std;
long long n,p,a[5000100],b[5000100],x,y,z,minn=500000001;
int main(){
	cin>>n>>p;
	for(long long i=0;i<n;i++){
		cin>>a[i];
	}
	for(long long i=0;i<p;i++){
		cin>>x>>y>>z;
		b[x-1]+=z;
		b[y]-=z;
	}
	for(long long i=0;i<n;i++){
		b[i]+=b[i-1];
		a[i]+=b[i];
		if(minn>a[i]){
			minn=a[i];
		}
	}
	cout<<minn;
	return 0;
}

#include<bits/stdc++.h>
using namespace std;
long long n,p,a[5000100],x,y,z,minn=500000001;
int main(){
	cin>>n>>p;
	for(long long i=0;i<n;i++){
		cin>>a[i];
	}
	for(long long i=0;i<p;i++){
		cin>>x>>y>>z;
		a[x-1]+=z;
		a[y]-=z;
	}
	for(long long i=0;i<n;i++){
		a[i]+=b[i-1];
		if(minn>a[i]){
			minn=a[i];
		}
	}
	cout<<minn;
	return 0;
}