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 Problemhttp://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 IIhttp://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 Inquiryhttp://acm.hdu.edu.cn/showproblem.php?pid=1047import 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+Bhttp://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 Fractionshttp://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.Exponentiationhttp://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0if(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)