一个赛马算法

原题：

25匹马，5条跑道，怎样能用最快方式，得到最快的三匹马，假设每匹马的体力保持不变，速度固定。

 

解法，堆排序，如下：package org.algorithm.search; import java.util.ArrayList; import java.util.Collections; import java.util.HashSet; import java.util.Iterator; import java.util.List; import java.util.Random; import java.util.Set; import java.util.Stack; /** * @author yuewei.wangyw */ public class FindFastestHorse { /** 跑的次数 **/ public static int times = 0; /** * 获得最快的那一匹 * * @param rootHorse 虚拟节点（最快的那一匹马） * @param runWaySize 跑道个数 * @return */ public static Horse findMax(Horse rootHorse, int runWaySize) { // 跑道 List<Horse> runWay = new ArrayList<Horse>(); // 比rootHorse 慢的马 List<Horse> slowerHorses = rootHorse.getSlowerHorses(); // 附加的比较的马匹，当比rootHorse 慢的马分组不够是，需要找更慢的马，进行比较，从而减少比较次数 List<Horse> additionHorses = new ArrayList<Horse>(); // 堆栈，用来实现查找下一匹马的递归实现 Stack<Horse> stack = new Stack<Horse>(); // 跑道个数 int size = runWaySize; // 直到找到最快的马 while (slowerHorses.size() > 1) { // 清除跑道 runWay.clear(); // 清除栈 stack.clear(); // 重置 size = runWaySize; // 对比当前rootHorse慢的马进行分组 for (Iterator<Horse> iter = slowerHorses.iterator(); iter.hasNext() && size-- > 0;) { Horse horse = iter.next(); runWay.add(horse); stack.add(horse); iter.remove(); } // 一旦分组不够，则取更慢的马 if (size > 0) { // 要么已经选够了马，要么没有马可以选 while (size > 0 && stack.size() > 0) { Horse currentNode = stack.pop(); // 选更慢的马 for (Iterator<Horse> iter = currentNode.getSlowerHorses().iterator(); iter.hasNext() && size-- > 0;) { Horse horse = iter.next(); additionHorses.add(horse); stack.add(horse); iter.remove(); } } // 更慢的马，加入到比赛队列 runWay.addAll(additionHorses); } // 开始赛马 Collections.sort(runWay); times++; // 建立马匹之间的关系 for (int i = 0; i < runWay.size() - 1; i++) { runWay.get(i).getSlowerHorses().add(runWay.get(i + 1)); } // 将当前比较队列中最快的马，加入到比rootHorse慢的马队中 slowerHorses.add(runWay.get(0)); System.out.println(">>>>第" + times + "次:"); rootHorse.print(); } // 得到最快的马，堆排序算法 return slowerHorses.get(0); } /** * @param rootHorse * @param runWaySize 跑道个数 * @param maxCount 最快马的个数 */ public static void find(Horse rootHorse, int runWaySize, int maxCount) { int i = 1; while (maxCount-- > 0) { rootHorse = findMax(rootHorse, runWaySize); System.out.println("--------第" + i++ + "名:" + rootHorse.getValue()); } } public static void main(String args[]) { List<Horse> horses = Race.getHourses(); for (int i = 0; i < horses.size(); i++) { System.out.print(horses.get(i).getValue()); System.out.print(" "); } Horse horse = new Horse(); horse.setValue(100); horse.setSlowerHorses(horses); System.out.println(" "); find(horse, 5, 3); } } /** * 赛马对象数据结构 * * @author yuewei.wangyw */ class Horse implements Comparable<Horse> { private int value; private List<Horse> slowerHorses; public Horse(){ slowerHorses = new ArrayList<Horse>(); } public List<Horse> getSlowerHorses() { return slowerHorses; } public void setSlowerHorses(List<Horse> slowerHorses) { this.slowerHorses = slowerHorses; } public int getValue() { return value; } public void setValue(int value) { this.value = value; } @Override public int compareTo(Horse o) { if (o.value > this.value) { return 1; } else if (o.value < this.value) { return -1; } else { return 0; } } private void print(int level) { for (int i = 0; i < level; i++) { System.out.print("| "); } System.out.print("+"); System.out.println(value); for (int i = 0; i < slowerHorses.size(); i++) { slowerHorses.get(i).print(level + 1); } } public void print() { print(0); } } /** * 生成马队 * * @author yuewei.wangyw */ class Race { public static List<Horse> getHourses() { List<Horse> hourses = new ArrayList<Horse>(); Random random = new Random(); random.setSeed(100); int rad = 0; Set<Integer> set = new HashSet<Integer>(); while (hourses.size() < 25) { rad = random.nextInt(1024) % 25; if (!set.contains(rad)) { set.add(rad); Horse horse = new Horse(); horse.setValue(rad + 1); hourses.add(horse); } } return hourses; } }

 

运行结果

15 3 25 8 9 4 23 11 19 14 5 18 24 22 13 1 17 16 7 6 12 10 21 2 20 
>>>>第1次:
+100
| +4
| +23
| +11
| +19
| +14
| +5
| +18
| +24
| +22
| +13
| +1
| +17
| +16
| +7
| +6
| +12
| +10
| +21
| +2
| +20
| +25
| | +15
| | | +9
| | | | +8
| | | | | +3
>>>>第2次:
+100
| +5
| +18
| +24
| +22
| +13
| +1
| +17
| +16
| +7
| +6
| +12
| +10
| +21
| +2
| +20
| +25
| | +15
| | | +9
| | | | +8
| | | | | +3
| +23
| | +19
| | | +14
| | | | +11
| | | | | +4
>>>>第3次:
+100
| +1
| +17
| +16
| +7
| +6
| +12
| +10
| +21
| +2
| +20
| +25
| | +15
| | | +9
| | | | +8
| | | | | +3
| +23
| | +19
| | | +14
| | | | +11
| | | | | +4
| +24
| | +22
| | | +18
| | | | +13
| | | | | +5
>>>>第4次:
+100
| +12
| +10
| +21
| +2
| +20
| +25
| | +15
| | | +9
| | | | +8
| | | | | +3
| +23
| | +19
| | | +14
| | | | +11
| | | | | +4
| +24
| | +22
| | | +18
| | | | +13
| | | | | +5
| +17
| | +16
| | | +7
| | | | +6
| | | | | +1
>>>>第5次:
+100
| +25
| | +15
| | | +9
| | | | +8
| | | | | +3
| +23
| | +19
| | | +14
| | | | +11
| | | | | +4
| +24
| | +22
| | | +18
| | | | +13
| | | | | +5
| +17
| | +16
| | | +7
| | | | +6
| | | | | +1
| +21
| | +20
| | | +12
| | | | +10
| | | | | +2
>>>>第6次:
+100
| +25
| | +15
| | | +9
| | | | +8
| | | | | +3
| | +24
| | | +22
| | | | +18
| | | | | +13
| | | | | | +5
| | | +23
| | | | +19
| | | | | +14
| | | | | | +11
| | | | | | | +4
| | | | +21
| | | | | +20
| | | | | | +12
| | | | | | | +10
| | | | | | | | +2
| | | | | +17
| | | | | | +16
| | | | | | | +7
| | | | | | | | +6
| | | | | | | | | +1
--------第1名:25
>>>>第7次:
+25
| +24
| | +23
| | | +21
| | | | +20
| | | | | +12
| | | | | | +10
| | | | | | | +2
| | | | +17
| | | | | +16
| | | | | | +7
| | | | | | | +6
| | | | | | | | +1
| | | +22
| | | | +18
| | | | | +13
| | | | | | +5
| | | | +19
| | | | | +14
| | | | | | +11
| | | | | | | +4
| | | | | +15
| | | | | | +9
| | | | | | | +8
| | | | | | | | +3
--------第2名:24
--------第3名:23