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codeforces--C - Anya and Ghosts(贪心)
Description
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.
Sample Input
1 8 310
3
2 10 15 8
1
1 1 310
-1
Hint
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：给出n个鬼访问的时间，和每个蜡烛可以持续的时间，每次访问最少需要的点燃的蜡烛数。问一共最少需要几个蜡烛。
将每个蜡烛的点燃的时间尽量靠近访问的时间，所以，统计第i个访问时点燃的蜡烛，如果少于r，那么要访问的时间开始，向前遍历，找出最近的可以点燃蜡烛的时刻，这样可以保证使用的蜡烛最少。
注意
1、可以在子夜之前点蜡烛，所以要将时间右移。
2、蜡烛持续的时间t和点燃的时间j的关系为，j时刻点蜡烛，j+1到j+t时刻蜡烛亮着。
#include <cstdio>#include <cstring>#include <algorithm>using namespace std ;int a[400] , k[2000] , flag[2000] ;int main(){ int m , t , r , num , i , j , ans ; while( scanf("%d %d %d", &m, &t, &r) != EOF ) { memset(k,0,sizeof(k)) ; memset(flag,0,sizeof(flag)) ; num = 0 ; ans = 0 ; for(i = 0 ; i < m ; i++) { scanf("%d", &a[i] ) ; a[i] += 1000 ; //flag[ a[i] ] = 1 ; } for(i = 0 ; i < m ; i++) { if( num < r ) { for(j = a[i]-1 ; j >= a[i]-t ; j--) { if( flag[j] == 0 ) { flag[j] = 1 ; k[j+1] += 1 ; k[j+1+t] += -1 ; num++ ; ans++ ; } if( num == r ) break ; } if( num < r ) break ; } for(j = a[i]+1 ; i < m-1 && j <= a[i+1] ; j++) num += k[j] ; } if( num < r ) printf("-1\n") ; else printf("%d\n", ans) ; } return 0 ;}codeforces--C - Anya and Ghosts(贪心)