Map的使用:
1 public class Main 2 { 3 public long factorial(int n){ 4 if(n<=1) 5 return 1; 6 return n * factorial(n-1); 7 } 8 9 public long func(String line){ 10 HashMap<Character, Integer> map = new HashMap<Character, Integer>(); 11 for(int i=0;i<line.length();i++){ 12 Character c = line.charAt(i); 13 if(map.containsKey(c)) 14 map.put(c, map.get(c)+1); //修改Map的元素值 15 else 16 map.put(c, 1); 17 } 18 //访问Map 19 long tmp = 1; 20 for(Character key : map.keySet()){ 21 int val = map.get(key); 22 tmp *= factorial(val); 23 } 24 25 return factorial(line.length()) / tmp; 26 } 27 28 29 public static void main(String[] args) 30 { 31 Main ob = new Main(); 32 Scanner scan = new Scanner(System.in); 33 while(scan.hasNextLine()){ 34 System.out.println(ob.func(scan.nextLine())); 35 } 36 } 37 }
匹配一个或多个空格:scan.nextLine().split("\\s+");
大部分内置类均位于java.lang.*、java.util.*、java.io.*包中
格式化输出的方法:
1 System.out.println("x = " + x + ", y = " + y); 2 // printf()方式 3 System.out.printf("x = %d, y = %f\n", x, y); 4 // format()方式 5 System.out.format("x = %d, y = %f\n", x, y);
scan有直接返回大数的方法,无需通过String创建大数。
数组填充:https://www.runoob.com/java/arrays-fill.html
当内存超了,标志数组可以考虑用BitSet:
1 BitSet arr = new BitSet(n); 2 arr.set(0, n, true); 3 arr.get(0)
在处理string和int交叉输入时,最好统一用nextLine()获取行,利用string.split(‘\\s+‘)划分,然后转成int
自定义比较对象:https://blog.csdn.net/qq_36785612/article/details/79935552
1 import java.util.Arrays; 2 import java.util.Comparator; 3 import java.util.Scanner; 4 5 public class Main 6 { 7 public void func(Score[] countryList){ 8 Arrays.sort(countryList, new MyCompare()); 9 //从大到小打印 10 for(int i=countryList.length-1;i>=0;i--) 11 System.out.println(countryList[i].contouryName); 12 } 13 14 public static void main(String[] args) 15 { 16 Main obj = new Main(); 17 Scanner scan = new Scanner(System.in); 18 while(scan.hasNextLine()){ 19 int num = Integer.parseInt(scan.nextLine()); 20 Score[] countryList = new Score[num]; 21 for(int i=0;i<num;i++){ 22 String line = scan.nextLine(); 23 String[] strList = line.split("\\s+"); 24 Score country = new Score(strList[0], Integer.parseInt(strList[1]), 25 Integer.parseInt(strList[2]), Integer.parseInt(strList[3])); 26 countryList[i] = country; 27 } 28 obj.func(countryList); 29 } 30 } 31 } 32 33 class Score{ 34 public String contouryName; 35 public int goldScore; 36 public int sliverScore; 37 public int bronzeScore; 38 39 Score(){ 40 this.contouryName = ""; 41 this.goldScore = 0; 42 this.sliverScore = 0; 43 this.bronzeScore = 0; 44 } 45 46 Score(String contouryName, int goldScore, int sliverScore, int bronzeScore){ 47 this.contouryName = contouryName; 48 this.goldScore = goldScore; 49 this.sliverScore = sliverScore; 50 this.bronzeScore = bronzeScore; 51 } 52 } 53 54 class MyCompare implements Comparator<Score>{ 55 @Override 56 public int compare(Score a, Score b){ 57 if(a.goldScore > b.goldScore) 58 return 1; 59 else if(a.goldScore == b.goldScore){ 60 if(a.sliverScore > b.sliverScore) 61 return 1; 62 else if(a.sliverScore == b.sliverScore){ 63 if(a.bronzeScore > b.bronzeScore) 64 return 1; 65 else if(a.bronzeScore == b.bronzeScore) 66 return a.contouryName.compareTo(b.contouryName); 67 } 68 } 69 return -1; 70 } 71 }
java中的栈类:
1 import java.util.Stack;
求最大公约数:辗转相除法。
表达式的计算:
建立两个栈:一个a存数字,一个b存运算符。
从左向右遍历,若为数字直接入a,若为运算符与b栈顶比较:若优先级大则入栈b;否则
对List排序:
1 import java.util.Collections; 2 Collections.sort(list);
注意string.replaceAll才支持正则表达式,string.replace不支持.
1 String strM = mStr.replaceAll("\\s+", "").toLowerCase();
去除string开头结尾的空格和换行符:
1 str.trim()
将int转成BigInterger:
1 BigInteger bi = BigInteger.valueOf(myInteger.intValue());
对于高精度的double小数或大数,直接利用toString()转成String,或直接打印,均会以科学计数法输出。解决办法:
1 BigDecimal bigA = new BigDecimal(a); 2 BigDecimal res = bigA.pow(b); 3 String sRes = res.stripTrailingZeros().toPlainString(); //去除末尾无效0
char转int不一定要强制转换,但是int转char要强制转换。
判断数组中是否存在重复元素:
1 public static boolean hasRepeat(String[] pInStr){ 2 HashSet<String> hashSet = new HashSet<>(); 3 for(int i=0;i<pInStr.length;i++){ 4 hashSet.add(pInStr[i]); 5 } 6 if(hashSet.size() == pInStr.length){ 7 return false; 8 } else{ 9 return true; 10 } 11 }
判断数组中是否包含某个元素:
1 Arrays.asList(pInStr).contains(FirstState)
对ArrayList动态数组排序:
1 ArrayList<String> leftList = new ArrayList<>(); 2 ArrayList<String> rightList = new ArrayList<>(); 3 for(int i=0;i<pInStr.length;i++){ 4 if(FirstState.compareTo(pInStr[i])<=0){ 5 leftList.add(pInStr[i]); 6 } else{ 7 rightList.add(pInStr[i]); 8 } 9 } 10 Collections.sort(leftList); 11 Collections.sort(rightList);
对String[]排序:
Arrays.sort(strList); //无返回值
原文地址:https://www.cnblogs.com/luckyboylch/p/12327316.html