Why RE on #9?玄关

#include<bits/stdc++.h>

using namespace std;

const int N = 550;

long long n , k , a[N] , sum = 0 , minn = 1e11;

int lef[N] , rig[N];

bool check(int x)
{
	int group = k , size = x;
	rig[k] = n;
	for (int i = n;i >= 1;i--)
	{
		if (size < a[i])
		{
			lef[group] = i+1;
			rig[group-1] = i; 
			group--;
			size = x - a[i];
		}
		else
		{
			size -= a[i];
		}
	}lef[1] = 1;
	if (group >= 1)return true;
	else return false;
	
}

int main()
{
	cin >> n >> k;
	for (int i = 1;i <= n;i++)cin >> a[i];
	for (int i = 1;i <= n;i++)sum += a[i] , minn = min(minn , a[i]);
	int l = minn , r = sum;
	while(l < r)
	{
		int mid = (l + r) >> 1;
		if (check(mid))r = mid;
		else l = mid + 1;
	} 
	check(l);
	for (int i = 1;i <= k;i++)
	{
		cout << lef[i] << ' ' << rig[i] << endl; 
	}
	return 0;
}