hdu 5163 前缀和+枚举

#include <iostream>
#include <algorithm>
#include <cstdio>
#include <cstring>
#define MAX 100007

using namespace std;

long long  sum[MAX],ans;

int main ( )
{
	int t,n,m,start,end,begin;
	scanf ( "%d" , &t );
	while ( t-- )
	{
		scanf ( "%d%d" , &n , &m );
		sum[1] = 0;
		for ( int i = 2 ; i <= n ; i++ )
			scanf ( "%lld" , &sum[i] );
		for ( int i = 2 ; i <= n; i++ )
			sum[i] = sum[i]+sum[i-1];
		for ( int i = 1 ; i <= m ; i++ )
		{
			scanf ( "%d%d" , &start , &end );
			begin = (i-1)%n+1;
			if ( begin <=start && start <= end )
					ans = sum[end] - sum[begin];
			if ( begin > start && start <= end )
					ans = 2*sum[n]-sum[begin]+sum[end];
			if (  end < start )
					ans = 2*sum[n]-sum[begin]-sum[end];
			printf ( "%lld\n" , ans );
		}
	}
}