水題一個，兩個排序解決問題

#include <cstdio>
#include <cstring>
#include <algorithm>
using namespace std;
int main()
{
	int n,m,sum;
	int head[20005]={0};
	int loo[20005]={0};
	while (~scanf ("%d %d",&n,&m)&&n&&m)
	{
		sum=0;
		memset (head,0,sizeof(head));
		memset (loo,0,sizeof (loo));
		for (int i=0;i<n;i++)
			scanf ("%d",&head[i]);
		for (int i=0;i<m;i++)
			scanf ("%d",&loo[i]);
		sort (loo,loo+m);
		sort (head,head+n);
		int i=0,j=0;
		bool flag=true;
		if (m<n)//騎士的數量少於惡龍頭的數量，一定無解 
			flag=false;	
		while (i<n&&flag)
		{//為惡龍的每一個頭找一個花費最小的騎士 
			while (j<m&&loo[j]<head[i])
				j++;
			if (m-j<n-i)
			{
				flag=false;
				break;
			}
			if (loo[j]>=head[i])
			{
				sum+=loo[j];
				i++,j++;
			}	
		}
		if (flag)
			printf ("%d\n",sum);
		else
			printf ("Loowater is doomed!\n");
	}
	return 0;
}