codeforces-508C-Anya and Ghosts【贪心】【思维】

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概述

题目链接：点击打开链接

Anya loves to watch horror movies. In the best traditions of horror, she will be visited by m ghosts tonight. Anya has lots of candles prepared for the visits, each candle can produce light for exactly t seconds. It takes the girl one second to light one candle. More formally, Anya can spend one second to light one candle, then this candle burns for exactly t seconds and then goes out and can no longer be used.

For each of the m ghosts Anya knows the time at which it comes: the i-th visit will happen wi seconds after midnight, all wi's are distinct. Each visit lasts exactly one second.

What is the minimum number of candles Anya should use so that during each visit, at least r candles are burning? Anya can start to light a candle at any time that is integer number of seconds from midnight, possibly, at the time before midnight. That means, she can start to light a candle integer number of seconds before midnight or integer number of seconds after a midnight, or in other words in any integer moment of time.

Input

The first line contains three integers m, t, r (1 ≤ m, t, r ≤ 300), representing the number of ghosts to visit Anya, the duration of a candle's burning and the minimum number of candles that should burn during each visit.

The next line contains m space-separated numbers wi (1 ≤ i ≤ m, 1 ≤ wi ≤ 300), the i-th of them repesents at what second after the midnight the i-th ghost will come. All wi's are distinct, they follow in the strictly increasing order.

Output

If it is possible to make at least r candles burn during each visit, then print the minimum number of candles that Anya needs to light for that.

If that is impossible, print - 1.

   Examples 
 
     input 
   
1 8 3
10

     output 
   
3

     input 
   
2 10 1
5 8

     output 
   
1

     input 
   
1 1 3
10

     output 
   
-1

Note

Anya can start lighting a candle in the same second with ghost visit. But this candle isn't counted as burning at this visit.

It takes exactly one second to light up a candle and only after that second this candle is considered burning; it means that if Anya starts lighting candle at moment x, candle is buring from second x + 1 to second x + t inclusively.

In the first sample test three candles are enough. For example, Anya can start lighting them at the 3-rd, 5-th and 7-th seconds after the midnight.

In the second sample test one candle is enough. For example, Anya can start lighting it one second before the midnight.

In the third sample test the answer is - 1, since during each second at most one candle can burn but Anya needs three candles to light up the room at the moment when the ghost comes.

题目大意：一个人要遇到m只鬼，遇到每只鬼要的时间为w[i]，他的蜡烛能亮t秒，遇到一只鬼要至少有r支蜡烛亮着，他点燃蜡烛要1s，点燃的时间不算燃烧的时间，求他最少要带多少根蜡烛，要不存在解输出－1

题目分析：按区间模拟，首先要判断的是当t小于r时无解，因为点燃也要1s，因此不可能存在一个时刻让r支蜡烛都亮着，我们应尽量保证蜡烛点燃的时刻离鬼来的时刻近，所以我们先找遇到第一个鬼的前1秒点一支蜡烛，假设此时为时刻t0则其后t0 + 1 + t的时间这根蜡烛都亮着，则这段区间标记一下，若此时不足以过第一个鬼则再遇到其前的第2秒再点一根，依次前推，注意当t0 + 1 + i小于0时，时间为负，不计积累量

#include<cstdio>
#include<cstring>
int ghost[3333]; // 刚开始开的容量为 333 一直 WA 
int mark[3333]; // 记录某一时间点的亮着的蜡烛数量 
int main()
{
	int m,t,r;
	while(~scanf("%d %d %d",&m,&t,&r))
	{
		for(int i=0;i<m;i++)
			scanf("%d",&ghost[i]);
		if(t<r)
		{
			printf("-1n");
			continue;
		}
		memset(mark,0,sizeof(mark));
		int ans=0;
		for(int i=0;i<m;i++)
		{
			for(int j=ghost[i]-1;mark[ghost[i]]<r;j--)
			{
				for(int k=j+1;k<=j+t;k++)
				{
					if(k>=0) // j可能会为 0 
					{
						mark[k]++;
					}
				}
				ans++;
			}
		}
		printf("%dn",ans);
	}
	return 0;
}