Java做acm所需要的基础知识之排序问题

Java做acm所需要的基础知识。

以前做acm的题都是用C/C++来写代码的，在学习完Java之后突然感觉Java中的方法比C/C++丰富很多，所以就整理一下平时做题需要用到的Java基础知识。

1、Arrays.sort()

（1）数字排序

int[] num =new int[]{4,2,3,5,-8,5,2,3};

Arrays.sort(num);

for(int i = 0; i < 8;i++)

System.out.print(num[i]+”,”);

输出结果：-8,2,2,3,3,4,5,5,

（2）字符串排序（先大写后小写原则）

String[] s = new String[]{"Z","a","A","z"};

Arrays.sort(s);

for(int i = 0; i < 4;i++)

System.out.print(s[i] +",");

输出结果：A,Z,a,z,

（3）严格按照字母表排序（即忽略大小写）

String[] s = new String[]{"Z","a","A","z"};

Arrays.sort(s,String.CASE_INSENSITIVE_ORDER);

for(int i = 0; i < 4;i++)

System.out.print(s[i] +",");

输出结果：a,A,Z,z,

（4）忽略大小写反向排序

String[] s = new String[]{"Z","a","A","z"};

Arrays.sort(s,String.CASE_INSENSITIVE_ORDER);

Collections.reverse(Arrays.asList(s));

for(int i = 0; i < 4;i++)

System.out.print(s[i] +",");

输出结果：z,Z,A,a,

（5）对象的排序（类似于C中的结构体的排序）

 import java.util.Arrays;
          import java.util.Comparator;
           public class Main
           {
               public static void main(String[] args)
               {
                  Dogd1 = new Dog("dog1",1);
                  Dogd2 = new Dog("dog2",2);
                  Dogd3 = new Dog("dog3",3);
                  Dogd4 = new Dog("dog4",4);
                  Dogd5 = new Dog("dog5",5);
                  Dog[]dogs = new Dog[] {d1,d2,d3,d4,d5};
                  Arrays.sort(dogs,new ByWeightComparator());
                  for(int i = 0; i <dogs.length; i++)
                  {
                      Dog dog = dogs[i];
                      System.out.print(dog.getName()+",");
                  }
               }
           }
           class Dog //定义一个“狗类”
           {
               private String name;
               private int weight;
               public Dog(String name, int weight)
               {
              this.setName(name);
              this.weight = weight;
               }
               public int getWeight()
               {
              return weight;
               }
               public void setWeight(int weight)
               {this.weight = weight;}
               public void setName(Stringname)
               {this.name = name;}
               public String getName()
               {return name;}
           }
           class ByWeightComparator implements Comparator
           {
               public final int compare(Object pFirst, Object pSecond)
               {
                  int aFirstWeight = ((Dog)pFirst).getWeight();
                  int aSecondWeight = ((Dog)pSecond).getWeight();
                  int diff = aFirstWeight - aSecondWeight;
                  if(diff >= 0)
                      return -1;
                  else if(diff < 0)
                      return 1;
                  return 0;
               }
           }

输出结果：dog5,dog4,dog3,dog2,dog1,

未完待续。。。。。。