POJ2010 贪心优先队列

c头牛,需要选n头（奇数）；学校总共有f的资金，
每头牛分数score和学费cost，问合法招生方案中,中间分数（即排名第(n+1)/2）最高的是多少。


n头牛按照先score后cost从小到大排序；
枚举中间score的牛,  预处理左边与右边的最小花费和。
预处理直接优先队列贪心

public class Main {
	public static void main(String[] args) {
		new Task().solve();
	}
}

class Task {
	Queue<Integer> q = new PriorityQueue<Integer>(1,
			new Comparator<Integer>() {
				@Override
				public int compare(Integer o1, Integer o2) {
					return (o1 > o2) ? -1 : ((o1 == o2) ? 0 : 1) ;  
				}
			}
	);
	
	class Node implements Comparable<Node>{
		int score ;
		int cost ;
		Node(int score , int cost){
			this.score = score  ;
			this.cost = cost ;
		}
		@Override
		public int compareTo(Node o) {
			if(score != o.score)
				return score < o.score ? -1 : 1 ;
			return (cost < o.cost) ? -1 : (cost == o.cost ? 0 : 1) ;
		}
		@Override
		public String toString() {
			return "Node [score=" + score + ", cost=" + cost + "]";
		}
		
	}
	
	void solve() {
		int n = in.nextInt() ;
		int c = in.nextInt() ;
		int f = in.nextInt() ;
		Node[] node = new Node[c+1] ;
		int[] minCostLeft = new int[c+1] ;
		int[] minCostRight = new int[c+1] ;
		
		for(int i = 1 ; i <= c ; i++){
			node[i] = new Node(in.nextInt() , in.nextInt()) ;
		}
        Arrays.sort(node , 1 , 1+c) ;
        int half = n/2  , sumCost = 0 ;
        int begin = half+1 , end = c - half  ;
        q.clear() ;
        for(int i = 1 ; i <= c ; i++){
        	if(q.size() > half) sumCost -= q.poll() ;
        	if(i >= begin) minCostLeft[i] = sumCost ;
        	sumCost += node[i].cost ;
        	q.add(node[i].cost) ;
        }
        q.clear() ;
        sumCost = 0 ;
        for(int i = c ; i >= 1 ; i--){
        	if(q.size() > half) sumCost -= q.poll() ;
        	if(i <= end) minCostRight[i] = sumCost ;
        	sumCost += node[i].cost ;
        	q.add(node[i].cost) ;
        }
        
        int res = -1 ;
        for(int i = end ; i >= begin ; i--){
        	if(node[i].cost + minCostLeft[i] + minCostRight[i] <= f){
        		res = node[i].score ;
        		break ; 
        	}
        }
		out.print(res) ;
		out.flush() ;
	}

	InputReader in = new InputReader(System.in);
	PrintWriter out = new PrintWriter(System.out);
}

class InputReader {
	public BufferedReader reader;
	public StringTokenizer tokenizer;

	public InputReader(InputStream stream) {
		reader = new BufferedReader(new InputStreamReader(stream), 32768);
		tokenizer = new StringTokenizer("");
	}

	private void eat(String s) {
		tokenizer = new StringTokenizer(s);
	}

	public String nextLine() {
		try {
			return reader.readLine();
		} catch (Exception e) {
			return null;
		}
	}

	public boolean hasNext() {
		while (!tokenizer.hasMoreTokens()) {
			String s = nextLine();
			if (s == null)
				return false;
			eat(s);
		}
		return true;
	}

	public String next() {
		hasNext();
		return tokenizer.nextToken();
	}

	public int nextInt() {
		return Integer.parseInt(next());
	}

	public long nextLong() {
		return Long.parseLong(next());
	}

	public double nextDouble() {
		return Double.parseDouble(next());
	}

	public BigInteger nextBigInteger() {
		return new BigInteger(next());
	}

}