java算法每日一练

 描述：有一组数（43,14,6,9,3,27,38,19,5等）

排序：将最大的放在第一位，最小放在第二位，剩下的最大的放在第三位，最小的放在第四位，以此类推

输出排序结果

 

作为一个新手，首先看到题目感觉有点难，他不像一般的大小排序可以调用工具类直接排序。

仔细想想其实也不是那么的复杂：

1.难点1：本身是个无序的组合，如果是个排序好的数组，或许就没有那么难了

2.排完序后，只要按照最后一个放第一位，原来的第一位放在后面，下面的以此类推。

 

 

 

int[] a = new int[]{43,14,6,9,3,27,38,19,5};

Arrays.sort(a);

for (int i = 0,j=a.length-1; i <= j;)
{
System.out.println(a[j--]);
if(j==i)
{
System.out.println(a[i]);
}
if(j>i)
{
System.out.println(a[i++]);
}
}

 

 

按照上的思路很快就能实现功能了。

 

 

由此，复习一下最近用到的排序，最近的一个有个优先级排序的功能，具体的掠过：

功能描述大概是这样的：按照规则对对象进行优先级排序，相同的优先级需要随机返回。

 下面的列子中People中的leavl是对象的优先级的体现。

 

 

public class People
{
public People(String name,String leavl,String id)
{
this.id = id;
this.name = name;
this.leavl = leavl;
}

private String name;

public String getName()
{
return name;
}

public void setName(String name)
{
this.name = name;
}

public String getLeavl()
{
return leavl;
}

public void setLeavl(String leavl)
{
this.leavl = leavl;
}

public String getId()
{
return id;
}

public void setId(String id)
{
this.id = id;
}

private String leavl;

private String id;

}

 

 

 

 

public static void main(String[] args)
{
People people1 = new People("cxm",1,"1");
People people2 = new People("zxc",1,"2");
People people3 = new People("zxz",2,"3");
People people4 = new People("zxx",4,"4");
People people5 = new People("zxv",2,"5");
People people6 = new People("zxb",3,"6");
People people7 = new People("zxn",4,"7");
People people8 = new People("zxm",3,"8");

List<People> list = new ArrayList<People>();
list.add(people1);
list.add(people2);
list.add(people3);
list.add(people4);
list.add(people5);
list.add(people6);
list.add(people7);
list.add(people8);

Collections.sort(list, new Comparator<People>()
{
public int compare(People arg0, People arg1)
{
return arg0.getLeavl().compareTo(arg1.getLeavl());
}
});

Set<Integer> set = new HashSet<Integer>();
set.add(people1.getLeavl());
set.add(people2.getLeavl());
set.add(people3.getLeavl());
set.add(people4.getLeavl());
set.add(people5.getLeavl());
set.add(people6.getLeavl());
set.add(people7.getLeavl());
set.add(people8.getLeavl());

Map<Integer ,List<People>> map = new HashMap<Integer, List<People>>();
List<People> newList = null;
for(Integer i : set)
{
newList = new ArrayList<People>();
for(People people : list)
{
if(i.equals(people.getLeavl()))
{
newList.add(people);
}
}
map.put(i, newList);
}

List<People> returnList = new ArrayList<People>();
for(Map.Entry<Integer, List<People>> entry :map.entrySet() )
{
returnList.addAll(getNewOrderList(entry.getValue()));
}

for(People people : returnList)
{
System.out.println("name "+people.getName()+"   leavl "+people.getLeavl() +"   id "+people.getId());
}

}

private static List<People> getNewOrderList(List<People> value)
{
Random rand = new Random();
int listIndex = rand.nextInt(value.size());
List<People> returnList = new ArrayList<People>();
returnList.add(value.get(listIndex));
value.remove(listIndex);
returnList.addAll(value);
return returnList;
}

 

public static void main(String[] args)
{
People people1 = new People("cxm",1,"1");
People people2 = new People("zxc",1,"2");
People people3 = new People("zxz",2,"3");
People people4 = new People("zxx",4,"4");
People people5 = new People("zxv",2,"5");
People people6 = new People("zxb",3,"6");
People people7 = new People("zxn",4,"7");
People people8 = new People("zxm",3,"8");

List<People> list = new ArrayList<People>();
list.add(people1);
list.add(people2);
list.add(people3);
list.add(people4);
list.add(people5);
list.add(people6);
list.add(people7);
list.add(people8);

Collections.sort(list, new Comparator<People>()
{
public int compare(People arg0, People arg1)
{
return arg0.getLeavl().compareTo(arg1.getLeavl());
}
});

Set<Integer> set = new HashSet<Integer>();
set.add(people1.getLeavl());
set.add(people2.getLeavl());
set.add(people3.getLeavl());
set.add(people4.getLeavl());
set.add(people5.getLeavl());
set.add(people6.getLeavl());
set.add(people7.getLeavl());
set.add(people8.getLeavl());

Map<Integer ,List<People>> map = new HashMap<Integer, List<People>>();
List<People> newList = null;
for(Integer i : set)
{
newList = new ArrayList<People>();
for(People people : list)
{
if(i.equals(people.getLeavl()))
{
newList.add(people);
}
}
map.put(i, newList);
}

List<People> returnList = new ArrayList<People>();
for(Map.Entry<Integer, List<People>> entry :map.entrySet() )
{
returnList.addAll(getNewOrderList(entry.getValue()));
}

for(People people : returnList)
{
System.out.println("name "+people.getName()+"   leavl "+people.getLeavl() +"   id "+people.getId());
}

}

private static List<People> getNewOrderList(List<People> value)
{
Random rand = new Random();
int listIndex = rand.nextInt(value.size());
List<People> returnList = new ArrayList<People>();
returnList.add(value.get(listIndex));
value.remove(listIndex);
returnList.addAll(value);
return returnList;
}

 

上面运用的排序：

1.

Collections.sort(list, new Comparator<People>()

实现了优先级的排序

2.

 

 

 

 

 

Random rand = new Random();
int listIndex = rand.nextInt(value.size());
List<People> returnList = new ArrayList<People>();
returnList.add(value.get(listIndex));
value.remove(listIndex);
returnList.addAll(value);

 

 

 

这里最终使用的那个值可能是People中的Id,实现了同一个优先级的随机返回。

测试的结果如下：

 

name zxc   leavl 1   id 2          name cxm   leavl 1   id 1      name zxc   leavl 1   id 2
name cxm   leavl 1   id 1          name zxc   leavl 1   id 2      name cxm   leavl 1   id 1
name zxv   leavl 2   id 5          name zxz   leavl 2   id 3      name zxz   leavl 2   id 3
name zxz   leavl 2   id 3          name zxv   leavl 2   id 5      name zxv   leavl 2   id 5
name zxm   leavl 3   id 8          name zxb   leavl 3   id 6      name zxm   leavl 3   id 8
name zxb   leavl 3   id 6          name zxm   leavl 3   id 8      name zxb   leavl 3   id 6
name zxn   leavl 4   id 7          name zxn   leavl 4   id 7      name zxn   leavl 4   id 7
name zxx   leavl 4   id 4          name zxx   leavl 4   id 4      name zxx   leavl 4   id 4

 

 

 

 

 

 

 

 

 

 

 

 

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