ACM之java入门

一.输入

import java.io.BufferedInputStream;
import java.util.Scanner;

/**
 * 格式1：Scanner sc = new Scanner (new BufferedInputStream(System.in));
 * 格式2：Scanner sc = new Scanner (System.in);
 * 在读入数据量大的情况下，格式1的速度会快些。
 * 读一个整数： int n = sc.nextInt(); 相当于 scanf("%d", &n); 或 cin >> n; 
 * 读一个字符串：String s = sc.next(); 相当于 scanf("%s", s); 或 cin >> s; 
 * 读一个浮点数：double t = sc.nextDouble(); 相当于 scanf("%lf", &t); 或 cin >> t; 
 * 读一整行： String s = sc.nextLine(); 相当于 gets(s); 或 cin.getline(...); 
 * 判断是否有下一个输入可以用sc.hasNext()或sc.hasNextInt()或sc.hasNextDouble()或sc.hasNextLine()
 * @author admin
 *
 */
public class InputExample {
	public static void main(String args[]){
		//exampleOne();
		//exampleTwo();
		//exampleThree();
		exampleFour();
	}
	
	/**
	 * 例1：读入整数
	 * Input  输入数据有多组，每组占一行，由一个整数组成。 
	 * Sample Input 
	 * 56
	 * 67
	 * 100
	 * 123 
	 */
	private static void exampleOne(){
		Scanner sc = new Scanner(System.in);
		while(sc.hasNext()){
			int score = sc.nextInt();
			System.out.println(score);
		}
	}
	/**
	 * 例2：读入实数
	 * 输入数据有多组，每组占2行，第一行为一个整数N，指示第二行包含N个实数。
	 * Sample Input
	 * 4 
	 * 56.9  67.7  90.5  12.8 
	 * 5 
	 * 56.9  67.7  90.5  12.8 
	 */
	public static void exampleTwo(){
		Scanner sc = new Scanner(new BufferedInputStream(System.in));
		while(sc.hasNext()){
			int n = sc.nextInt();
			for(int i = 0; i < n; i++){
				double a = sc.nextDouble();
				System.out.println(a);
			}
		}
	}
	/**
	 * 例3：读入字符串【杭电2017 字符串统计】
	 * 输入数据有多行，第一行是一个整数n，表示测试实例的个数，后面跟着n行，每行包括一个由字母和数字组成的字符串。
	 * Sample Input  
	 * 2
	 * asdfasdf123123asdfasdf
	 * asdf111111111asdfasdfasdf
	 */
	public static void exampleThree(){
		Scanner sc = new Scanner(new BufferedInputStream(System.in));
		while(sc.hasNext()){
			int n = sc.nextInt();
			for(int i = 0; i < n; i++){
				String s = sc.next();
				System.out.println(s);
			}
		}
	}
	/**
	 * 例3：读入字符串【杭电2005 第几天？】
	 * 给定一个日期，输出这个日期是该年的第几天。 
	 * Input  输入数据有多组，每组占一行，数据格式为YYYY/MM/DD组成
	 * 1985/1/20
	 * 2006/3/12
	 */
	public static void exampleFour(){
		Scanner sc = new Scanner(new BufferedInputStream(System.in));
		while(sc.hasNext()){
			int md[] = {31, 27, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
			String str[] = sc.next().split("/");
			int year = Integer.parseInt(str[0]);
			int month = Integer.parseInt(str[1]);
			int day = Integer.parseInt(str[2]);
			int days = 0;
			for(int i = 0; i < month - 1; i++) days += md[i];
			days += day;
			if( month>2 && ( year%400 == 0 || (year%100 != 0 && year%4 == 0))) days++;
			System.out.println(days);
		}
	}
	
}

二.输出

import java.io.BufferedInputStream;
import java.text.DecimalFormat;
import java.text.NumberFormat;
import java.util.Scanner;

/**
 * 函数：
 * System.out.print(); 
 * System.out.println(); 
 * System.out.format();
 * System.out.printf();  
 * @author admin
 *
 */
public class OutputExample {
	public static void main(String[] args) {
		//exampleOne();
		exampleTwo();
	}
	/**
	 * 例4 杭电1170Balloon Comes!
	 * Give you an operator (+,-,*, / --denoting addition, subtraction, multiplication, division respectively) 
	 * and two positive integers, your task is to output the result. 
	 * Input
	 * Input contains multiple test cases. The first line of the input is a single integer T (0<T<1000) 
	 * which is the number of test cases. T test cases follow. Each test case contains a char C (+,-,*, /) 
	 * and two integers A and B(0<A,B<10000).Of course, we all know that A and B are operands and C is an operator. 
	 * Output
	 * For each case, print the operation result. The result should be rounded to 2 decimal places If 
	 * and only if it is not an integer.
	 * Sample Input
	 * 4
	 * + 1 2
	 * - 1 2
	 * * 1 2
	 * / 1 2
	 * Sample Output
	 * 3
	 * -1
	 * 2
	 * 0.50
	 */
	private static void exampleOne(){
		Scanner sc = new Scanner(new BufferedInputStream(System.in));
		while(sc.hasNext()){
			int t = sc.nextInt();
			for(int times = 0; times < t; times++){
				String c = sc.next();
				int a = sc.nextInt();
				int b = sc.nextInt();
				if(c.equals("+")) System.out.println(a+b);
				else if(c.equals("-")) System.out.println(a-b);
				else if(c.equals("*")) System.out.println(a*b);
				else System.out.format("%.2f", (a*1.0)/b).println();
			}
		}
	}
	
	/**
	 * 规格化的输出：
	 * 函数：
	 * 这里0指一位数字，#指除0以外的数字(如果是0，则不显示),四舍五入.
	 * DecimalFormat fd = new DecimalFormat("#.00#");
	 * DecimalFormat gd = new DecimalFormat("0.000");
	 * System.out.println("x =" + fd.format(x));
	 * System.out.println("x =" + gd.format(x));
	 */
	private static void exampleTwo(){
		NumberFormat   formatter   =   new   DecimalFormat( "000000"); 
        String  s  =   formatter.format(-1234.567);     //   -001235 
        System.out.println(s);
        formatter   =   new   DecimalFormat( "##"); 
        s   =   formatter.format(-1234.567);             //   -1235 
        System.out.println(s);
        s   =   formatter.format(0);                      //   0 
        System.out.println(s);
        formatter   =   new   DecimalFormat( "##00"); 
        s   =   formatter.format(0);                     //   00 
        System.out.println(s);

        formatter   =   new   DecimalFormat( ".00"); 
        s   =   formatter.format(-.567);               //   -.57 
        System.out.println(s);
        formatter   =   new   DecimalFormat( "0.00"); 
        s   =   formatter.format(-.567);              //   -0.57 
        System.out.println(s);
        formatter   =   new   DecimalFormat( "#.#"); 
        s   =   formatter.format(-1234.567);         //   -1234.6 
        System.out.println(s);
        formatter   =   new   DecimalFormat( "#.######"); 
        s   =   formatter.format(-1234.567);        //   -1234.567 
        System.out.println(s);
        formatter   =   new   DecimalFormat( ".######"); 
        s   =   formatter.format(-1234.567);       //   -1234.567 
        System.out.println(s);
        formatter   =   new   DecimalFormat( "#.000000"); 
        s   =   formatter.format(-1234.567);      //   -1234.567000 
        System.out.println(s);
        
        formatter   =   new   DecimalFormat( "#,###,###"); 
        s   =   formatter.format(-1234.567);      //   -1,235 
        System.out.println(s);
        s   =   formatter.format(-1234567.890);  //   -1,234,568 
        System.out.println(s);

        //   The   ;   symbol   is   used   to   specify   an   alternate   pattern   for   negative   values 
        formatter   =   new   DecimalFormat( "#;(#) "); 
        s   =   formatter.format(-1234.567);     //   (1235) 
        System.out.println(s);

        //   The   '   symbol   is   used   to   quote   literal   symbols 
        formatter   =   new   DecimalFormat( " '# '# "); 
        s   =   formatter.format(-1234.567);        //   - # 1235 
        System.out.println(s);
        formatter   =   new   DecimalFormat( " 'abc '# "); 
        s   =   formatter.format(-1234.567);      // - abc 1235
        System.out.println(s);
        
        formatter   =   new   DecimalFormat( "#.##%"); 
        s   =   formatter.format(-12.5678987);  
        System.out.println(s);
	}
	
}

三.字符串处理

/**
 * String 类用来存储字符串，可以用charAt方法来取出其中某一字节，计数从0开始： 
 * String a = "Hello"; // a.charAt(1) = 'e' 
 * 
 * 用substring方法可得到子串，如上例 
 * System.out.println(a.substring(0, 4)) // output "Hell" 
 * 注意第2个参数位置上的字符不包括进来。这样做使得 s.substring(a, b) 总是有 b-a个字符。 
 * 
 * 字符串连接可以直接用 + 号，如 
 * String a = "Hello"; 
 * String b = "world"; 
 * System.out.println(a + ", " + b + "!"); // output "Hello, world!" 
 * 
 * 如想直接将字符串中的某字节改变，可以使用另外的StringBuffer类。
 * @author admin
 *
 */
public class StringExample {

}

四.高精度

import java.io.BufferedInputStream;
import java.math.BigInteger;
import java.util.Scanner;

/**
 * BigInteger和BigDecimal可以说是acmer选择java的首要原因。
 * 函数：add, subtract, divide, mod, compareTo等，
 * 其中加减乘除模都要求是BigInteger(BigDecimal)和BigInteger(BigDecimal)之间的运算，
 * 所以需要把int(double)类型转换为BigInteger(BigDecimal)，用函数BigInteger.valueOf().
 * @author admin
 *
 */
public class HighPrecision {
	public static void main(String[] args) {
		Scanner cin = new Scanner (new BufferedInputStream(System.in));
        int a = 123, b = 456, c = 7890;
        BigInteger x, y, z, ans;
        x = BigInteger.valueOf(a); 
        y = BigInteger.valueOf(b); 
        z = BigInteger.valueOf(c);
        ans = x.add(y); System.out.println(ans);
        ans = z.divide(y); System.out.println(ans);
        ans = x.mod(z); System.out.println(ans);
        if (ans.compareTo(x) == 0) System.out.println("1");

	}
}

五.进制转换

/**
 * java很强大的一个功能。
 * 函数：
 * String st = Integer.toString(num, base); // 把num当做10进制的数转成base进制的st(base <= 35).
 * int num = Integer.parseInt(st, base); // 把st当做base进制，
 * 转成10进制的int(parseInt有两个参数,第一个为要转的字符串,第二个为说明是什么进制).  
 * BigInter m = new BigInteger(st, base); // st是字符串，base是st的进制.
 * @author admin
 *
 */
public class HexadecimalConversionExamp {

}

六.数组排序

import java.io.BufferedInputStream;
import java.util.Arrays;
import java.util.Scanner;

/**
 * 函数：Arrays.sort();
 * @author admin
 *
 */
public class ArraysSortExample {
	public static void main(String[] args) {
		Scanner cin = new Scanner (new BufferedInputStream(System.in));
        int n = cin.nextInt();
        int a[] = new int [n];
        for (int i = 0; i < n; i++) a[i] = cin.nextInt();
        Arrays.sort(a);
        for (int i = 0; i < n; i++) System.out.print(a[i] + " ");
        for (int i = n - 1; i >= 0; i--) System.out.print(a[i] + " ");

	}
}