NYOJ-12 喷水装置（二）

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NYOJ-12 喷水装置（二）

分析：贪心算法
对于输入的每个点,求出能覆盖住矩形的起点和终点,然后按起点排序,如果最小的起点和最大的终点都不能超过矩形的长度范围,则必定无解,取出起始点最靠前的点,然后记录下这个点的终点,遍历这个起点到终点范围内的所有其他的点,并挑选其中终点最靠后的那个点作为下一个终点的位置,并且计数器加一,继续向后遍历,如果有区间接不上,则表明无解,成功遍历到矩形最后,则直接输出计数器的值

代码如下：

import java.util.PriorityQueue;import java.util.Scanner;public class Main {    static class node implements Comparable<node>{        double l;        double r;        public node(double l, double r) {            this.l=l;            this.r=r;        }        @Override        public int compareTo(node o) {            return Double.compare(this.l, o.l);        }    }    public static void main(String[] args) {        Scanner sc=new Scanner(System.in);        int m, w, h;        PriorityQueue<node> q;        int n=sc.nextInt();        for(int i=0;i<n;++i){            m=sc.nextInt();            w=sc.nextInt();            h=sc.nextInt()/2;            q=new PriorityQueue<node>();            int count=0;            double tail, max;            for(int j=0;j<m;++j){                double tempm, tempr;                tempm=sc.nextInt();                tempr=sc.nextInt();                if(tempr>h){                    tempr=(double) Math.sqrt(tempr*tempr-h*h);                    q.add(new node(tempm-tempr, tempm+tempr));                }            }            max=tail=0;            node tempnode=null;            while(!q.isEmpty()){                while(!q.isEmpty()&&(tempnode=q.peek()).l<=tail){                    if(tempnode.r>max)                        max=tempnode.r;                    q.poll();                }                if(max!=tail){                    count++;                    tail=max;                    if(tail>=w)                        break;                }                else                    break;            }            if(tail<w)                System.out.println(0);            else                System.out.println(count);        }        sc.close();    }}

下面是一段别人的代码，结构大同小异，运行结果却比我的好得多，
所需时间是我的1/3.6，内存1/5，并不明白为什么(⊙_⊙)?求指教

import java.io.BufferedReader;import java.io.IOException;import java.io.InputStreamReader;import java.util.Comparator;import java.util.PriorityQueue;import java.util.StringTokenizer;public class Main {    static class Node {        double left;        double right;        public Node(double d, double e) {            this.left = d;            this.right = e;        }    }    static Comparator<Node> comparator = new Comparator<Node>() {        public int compare(Node o1, Node o2) {            return Double.compare(o1.left, o2.left);        }    };    public static void main(String[] args) throws IOException {        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));        StringTokenizer st;        int k = Integer.parseInt(br.readLine());        while (k-- > 0) {            st = new StringTokenizer(br.readLine());            int n = Integer.parseInt(st.nextToken());            double width = Double.parseDouble(st.nextToken());            double height = Double.parseDouble(st.nextToken()) / 2;            PriorityQueue<Node> arr = new PriorityQueue<Node>(n, comparator);            for (int i = 0; i < n; i++) {                st = new StringTokenizer(br.readLine());                double a = Double.parseDouble(st.nextToken());                double b = Double.parseDouble(st.nextToken());                if (b > height) {                    double len = Math.sqrt(b * b - height * height);                    arr.add(new Node(a - len, a + len));                }            }            double start = 0;            int count = 0;            boolean flag = false;            while (!arr.isEmpty()) {                double max = Double.MIN_VALUE;                Node node = null;                while (!arr.isEmpty() && arr.peek().left <= start) {                    if (arr.peek().right > max) {                        max = arr.peek().right;                        if (node != null)                            arr.remove(node);                        node = arr.peek();                    } else {                        arr.poll();                    }                }                if (max == Double.MIN_VALUE) {                    break;                }                if (node != null)                    arr.remove(node);                if (max > start) {                    start = max;                    count++;                }                if (start >= width) {                    flag = true;                    break;                }            }            System.out.println(flag ? count : 0);        }    }}

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