实在找不到原因了，和题解思路也是一样的

#include<bits/stdc++.h>
using namespace std;
using ll = long long;
const int N = 5*1e6+9;
ll a[N],d[N];

int main()
{
	ios::sync_with_stdio(0),cin.tie(0),cout.tie(0);
	ll n,p,res;cin >> n >> p;
	for(int i = 1;i <= n;i++)cin >> a[i];
	for(int i = 1;i <= n;i++)d[i] = a[i] - a[i-1];
	while(p--){
	ll x,y,z;cin >> x >> y >> z;
	d[x] += z;
	d[y + 1] -= z;
	}
	for(int i = 1;i <= n;i++)a[i] = d[i] + a[i - 1];
	for(int i = 1;i <= n;i++)res = min(res,a[i]);
	cout << res <<'\n';
	return 0;
}