JAVA 水题 练手

是时候学一下java了，然后就刷了几道题，贴上来以备以后忘记，要是能过方便大家更好不过了。

Scanner cin = new Scanner(System.in);//读入流

while(cin.hasNext())//cin.hasNext()返回bool型，如果流中还有数据返回真，类似于读到文件末尾

如果读入一个T代表组数 应该写成while(T-->0) 

a = cin.nextInt(); //读入整数
a = cin.nextBigInteger();//读入大数
a = cin.nextBigDecimal();//读入高精度大数

BigDecimal a; //高精度大数的定义

BigInteger a; //大数的定义
BigInteger fib[] = new BigInteger[501];//大数数组定义

大数之间可以直接运算、赋值，但是大数和其他类型的数则这不行。

所以大数初始化的时候一般是

a = BigInteger.valueOf(0); 或者 a = new BigInteger("0");

大数乘以非大数也是将其转换为大数再运算

eg:ans = ans.multiply(BigInteger.valueOf(i));

大数之间的比较：一般都是用compareTo 

 if(a.compareTo(BigDecimal.ZERO) == 0)

高精度大数除去后导0， 用stripTrailingZeros，但是还需要用 toPlainString，原因如下:

stripTrailingZeros 去除后导0 但是如果是数字大于10的话会转换成（eg：12500 会转换成 1.25E+4）

toPlainString 将1.25E+4转换成字符串 1.25E+4->12500

System.out.println(a.stripTrailingZeros().toPlainString());

1.A + B Problem

http://acm.hdu.edu.cn/showproblem.php?pid=1000

import java.math.*;import java.util.*;public class Main {    public static void main(String[] args) {                int a,b;        Scanner cin = new Scanner(System.in);        while(cin.hasNext())        {            a = cin.nextInt();            b = cin.nextInt();            System.out.println(a+b);        }    }}

2.A + B Problem II

http://acm.hdu.edu.cn/showproblem.php?pid=1002

import java.math.*;import java.util.*;public class Main {    public static void main(String[] args) {        int n, i;        Scanner cin = new Scanner(System.in);        BigInteger a,b;        n = cin.nextInt();        for(i = 1; i <= n; i++)        {            a = cin.nextBigInteger();            b = cin.nextBigInteger();            System.out.println("Case "+ i +":");            System.out.println(a + " + " + b + " = " + a.add(b));            if(i != n) System.out.println();        }     }}

3.N!
http://acm.hdu.edu.cn/showproblem.php?pid=1042

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

4.Integer Inquiry

http://acm.hdu.edu.cn/showproblem.php?pid=1047

import java.math.*;import java.util.*;public class Main {    public static void main(String[] args) {                Scanner cin = new Scanner(System.in);        int n = cin.nextInt();        for(int i = 1; i <= n; i++)        {            BigInteger sum = BigInteger.valueOf(0);            while(cin.hasNext())            {                BigInteger num = cin.nextBigInteger();                if(num.equals(BigInteger.ZERO)) break;                                sum = sum.add(num);            }            System.out.println(sum);            if(i != n) System.out.println();        }    }}

5.大明A+B
http://acm.hdu.edu.cn/showproblem.php?pid=1753

import java.math.*;import java.util.*;public class Main {    public static void main(String[] args) {                Scanner cin = new Scanner(System.in);        BigDecimal a,b;        while(cin.hasNext())        {            a = cin.nextBigDecimal();            b = cin.nextBigDecimal();            a = a.add(b);                        if(a.compareTo(BigDecimal.ZERO) == 0)                System.out.println("0");            else                System.out.println(a.stripTrailingZeros().toPlainString());        }    }}

6.Octal Fractions
http://poj.org/problem?id=1131

stripTrailingZeros 去除后导0 但是如果是数字大于10的话会转换成（eg：12500 会转换成 1.25E+4）

toPlainString 将1.25E+4转换成字符串 1.25E+4->12500

import java.math.*;import java.util.*;public class Main {        public static void main(String[] args)         {                String s;                BigDecimal eight = new BigDecimal(8);                Scanner cin = new Scanner(System.in);                while(cin.hasNext())                {                        s = cin.nextLine();                        BigDecimal ans = new BigDecimal(0);                        BigDecimal mul = new BigDecimal(1);                        for(int i = 2; i < s.length(); i++)                        {                                mul = mul.divide(eight);                                ans = ans.add(new BigDecimal(s.charAt(i) - '0').multiply(mul));                        }                        System.out.println(s + " [8] = " + ans.stripTrailingZeros().toPlainString() + " [10]");                }        }}

7.大菲波数http://acm.hdu.edu.cn/showproblem.php?pid=1715

读入一个T代表组数

while(T--)应该写成while(T-->0)

import java.math.*;import java.util.*;public class Main {    public static void main(String[] args)     {        BigInteger fib[] = new BigInteger[1001];        fib[0] = BigInteger.valueOf(0);        fib[1] = BigInteger.valueOf(1);        fib[2] = BigInteger.valueOf(1);        for(int i = 3; i <= 1000; i++)        {            fib[i] = fib[i-1].add(fib[i-2]);         }        Scanner cin = new Scanner(System.in);        int n;        n = cin.nextInt();        while(n-->0)        {            int num;            num = cin.nextInt();            System.out.println(fib[num]);        }    }}

8.How Many Fibs?
http://acm.hdu.edu.cn/showproblem.php?pid=1316

import java.math.*;import java.util.*;public class Main {    public static void main(String[] args)     {        BigInteger fib[] = new BigInteger[501];        fib[0] = BigInteger.valueOf(0);        fib[1] = BigInteger.valueOf(1);        fib[2] = BigInteger.valueOf(2);        for(int i = 3; i <= 480; i++)        {            fib[i] = fib[i-1].add(fib[i-2]);         }        Scanner cin = new Scanner(System.in);        int l  = 0, r = 0, i;        BigInteger a, b;        a = cin.nextBigInteger();        b = cin.nextBigInteger();        while(a.compareTo(fib[0]) != 0 || b.compareTo(fib[0]) != 0)        {            for(i = 1;; i++)            {                if(a.compareTo(fib[i]) <= 0)                 {                    l = i;                    break;                }            }            for(;; i++)            {                if(b.compareTo(fib[i]) < 0)                {                    r = i;                    break;                }            }                    System.out.println(r-l);            a = cin.nextBigInteger();            b = cin.nextBigInteger();        }    }}

9.Exponentiation
http://acm.hdu.edu.cn/showproblem.php?pid=1063

s.startsWith("0.") //startsWith 是判断s字符串开头是不是("0.") 分号中这个字符串

import java.math.*;import java.util.*;public class Main {    public static void main(String[] args)     {        Scanner cin = new Scanner(System.in);        while(cin.hasNext())        {            BigDecimal a, ans;            int b;            a = cin.nextBigDecimal();            b = cin.nextInt();            ans  = a;            for(int i = 2; i <= b; i++)                ans = ans.multiply(a);                        String s = ans.stripTrailingZeros().toPlainString();//去掉后导0            if(s.startsWith("0.")) //startsWith 是判断开头是不是("str") 分号中这个字符串                s = s.substring(1);            System.out.println(s);        }            }}

如果读入一个T代表组数

while(T--)应该写成while(T-->0)