java高精度,大数

package 高精度幂;
 
import java.math.BigDecimal;
import java.util.Scanner;
 
public class Main{
    public static void main(String[] args) {
        Scanner cin = new Scanner(System.in);
        while (cin.hasNext()) {
            BigDecimal bd = new BigDecimal(cin.next());
            BigDecimal result = bd.pow(cin.nextInt());
            String s = result.stripTrailingZeros().toPlainString(); //去掉尾零
            if(s.startsWith("0"))        //去掉首零
                s=s.substring(1);
            System.out.println(s);
        }
    }
    
}


2.HDU1042 N!

import java.math.*;
import java.util.*;
 
public class Main {
    public static BigInteger num;
 
    public static void main(String args[]) {
        Scanner cin = new Scanner(System.in);
        
        while (cin.hasNext()) {
            num = BigInteger.ONE;
            int n = cin.nextInt();
            num = BigInteger.ONE;
            for (int i = 1; i <= n; i++) {
                num= num.multiply(BigInteger.valueOf(i));
            }
            System.out.println(num);
        }
    }
}

4.HDU1753 加法

import java.math.BigDecimal;
import java.util.Scanner;
import java.util.*;
 
public class Main {
 
    public static void main(String[] args) {
        Scanner cin = new Scanner(System.in);
        while(cin.hasNext()){
            BigDecimal a=cin.nextBigDecimal();
            BigDecimal b=cin.nextBigDecimal();
            String s = a.add(b).stripTrailingZeros().toPlainString();
            System.out.println(s);
        }
 
    }
 
}

 

比较函数

 if(a.compareTo(b)<0)//此时由于a<b,则返回值小于0;
        {
            System.out.println("a<b");
        }
        if(b.equals(c))//此时由于b==c,则返回值等于0;
        {
            System.out.println("b==c");
        }
        if(d.compareTo(c)>0)//此时由于d>c,则返回值大于0;  
        {
            System.out.println("d>c");
        }

 

 

(4) 
对于输出浮点数保留几位小数的问题,可以使用DecimalFormat类, 

import java.text.*; 
DecimalFormat f = new DecimalFormat("#.00#"); 
DecimalFormat g = new DecimalFormat("0.000"); 
double a = 123.45678, b = 0.12; 
System.out.println(f.format(a)); 
System.out.println(f.format(b)); 
System.out.println(g.format(b)); 

这里0指一位数字,#指除0以外的数字。 

 

string中的字符串不可变,stringbuild或者stringbuffer中的可变,还有insert与append方法

 

reverse函数

package test1;

public class TestReverse {
public static void main(String[] args) {
String str2 = "Hello";
str2 = new StringBuffer(str2).reverse().toString();
System.out.println(str2);

String message = "Hello";
StringBuilder rev = new StringBuilder();
for (int i = message.length() - 1; i >= 0; i--)
rev.append(message.charAt(i));
System.out.println(rev.toString());

}

}

 

 

java中字符串String是不可以修改的,要修改只能转换为字符数组.

例程:

 

[java] view plain copy
 
 
 
 
  1. import java.io.*;  
  2. import java.math.*;  
  3. import java.util.*;  
  4. import java.text.*;  
  5. public class Main  
  6. {  
  7.     public static void main(String[] args)   
  8.     {  
  9.         int i;  
  10.         Scanner cin = new Scanner (new BufferedInputStream(System.in));  
  11.         String st = "abcdefg";  
  12.         System.out.println(st.charAt(0)); // st.charAt(i)就相当于st[i].  
  13.         char [] ch;  
  14.         ch = st.toCharArray(); // 字符串转换为字符数组.  
  15.         for (i = 0; i < ch.length; i++) ch[i] += 1;  
  16.         System.out.println(ch); // 输入为“bcdefgh”.  
  17. if (st.startsWith("a")) // 如果字符串以'0'开头.  
  18.         {  
  19.             st = st.substring(1); // 则从第1位开始copy(开头为第0位).  
  20.         }  
  21.     }  
  22. }  

 

函数:Arrays.sort();

例程:

 

[java] view plain copy
 
 
 
 
  1. import java.io.*;  
  2. import java.math.*;  
  3. import java.util.*;  
  4. import java.text.*;  
  5. public class Main  
  6. {  
  7.     public static void main(String[] args)   
  8.     {  
  9.         Scanner cin = new Scanner (new BufferedInputStream(System.in));  
  10.         int n = cin.nextInt();  
  11.         int a[] = new int [n];  
  12.         for (int i = 0; i < n; i++) a[i] = cin.nextInt();  
  13.         Arrays.sort(a);  
  14.         for (int i = 0; i < n; i++) System.out.print(a[i] + " ");  
  15.     }  
  16. }  

 

        

         1、Arrays.sort()
                   (1)数字排序
                                int[] num =newint[]{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)

package zoj3380;

import java.io.*;
import java.lang.reflect.Array;
import java.text.*;
import java.util.*;
import java.math.*;
public class Main
{
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int n = scanner.nextInt();
        student[] students = new student[10];
        for (int i = 0; i < n; i++) {
            String s = scanner.next();
            int a = scanner.nextInt();
            int b = scanner.nextInt();
            students[i] = new student(a, b, s);
        }
//        int len = students.;
        Arrays.sort(students,0, n, new Acomparator());
//排序必须保证每个里面都有元素,要不然会报错。
// Arrays.sort(students, new Acomparator()); for(int i = 0; i < n; i++) { System.out.println(students[i].getA()); } } } class student { private int a, b; private String s; public student(int a, int b, String s) { this.a = a; this.b = b; this.s = s; } public int getA() { return a; } public void setA(int a) { this.a = a; } public int getB() { return b; } public void setB(int b) { this.b = b; } public String getS() { return s; } public void setS(String s) { this.s = s; } } class Acomparator implements Comparator { @Override public int compare(Object o1, Object o2) { int a = ((student)o1).getA(); int b = ((student)o2).getA(); int c = a - b; if(c <= 0) return -1; else return 1; } }

 

 

posted @ 2019-06-17 20:15  downrainsun  阅读(1642)  评论(0编辑  收藏  举报