Java编程题

可以网上运行以下代码：java在线编程网站
（1） 如何判断一个字符串中某个字符出现的次数？(for循环)

public static void main(String[] args) {
    String str = "ABC123ABC";
    char searchChar = 'B';
    int count = 0;
    char[] charArray = str.toCharArray();
    for (char item : charArray) {
        if (item == searchChar) {
            count++;
        }
    }
    System.out.println("字符" + searchChar + "出现的次数为：" + count);
}

（2） 如何判断一个字符串中某个字符出现的次数？(replace())

import java.io.*;
class test  
{
	public static void main (String[] args) throws java.lang.Exception{
     String str = "ABC123ABC";
     String searchChar="B";
     String a=str.replace(searchChar,"");
     
    int count = str.length()-a.length();
    
    System.out.println("字符" + searchChar + "出现的次数为：" + count);
}
}

（3） Java两个有序数组合并为一个有序数组

public class MyClass {
    static void merge(int[] a, int[] b) {
        int l = a.length + b.length;
        int[] c = new int[l];
        int i = 0;
        int j = 0;
        int x = 0;

        while ((i < a.length) || (j < b.length)) {
            if ((i == a.length) && (j < b.length)) {
                c[x++] = b[j++];
            } else if ((i < a.length) && (j == b.length)) {
                c[x++] = a[i++];
            } else if (a[i] <= b[j]) {
                c[x++] = a[i++];
            } else if (a[i] > b[j]) {
                c[x++] = b[j++];
            }
        }

        for (int d : c) {
            System.out.print("\t" + d);
        }
    }

    public static void main(String[] args) throws java.lang.Exception {
        int[] a = { 1, 3, 5, 6, 15 };
        int[] b = { 1, 3, 4, 5, 7, 9 };
        merge(a, b);
    }
}

(5) 1000以内的质数并且个位十位百位加起来等于偶数

public class MyClass {
    static void find(int i) {
    int t=0;
    for(int k=1;k<=1000;k++){
      if(i%k!=0)
      t++;
      if(t==998){
      int j=i;
      int result=0;
      int sum=0;
      do{
          result=i%10; 
          sum+=result; 
          i=i/10; 
      } while(i!=0);
        if(sum%2==0){
            System.out.print(j+"\t");
            }
      }
  }}
 public static void main (String[] args) throws java.lang.Exception{
 for(int i=0;i<=1000;i++) {
      if(i==1)
      continue;
      find(i);
   }
 }
}

(6) 打印杨辉三角

public class MyClass {
    public static void main(String args[]) {
    int[][] a = new int[10][10];
   for (int i = 0; i <10 ; i++) {
            a[i][0]=1;
   }
   for (int i = 1; i <10 ; i++) {
      for (int j = 1; j <10 ; j++) {
         a[i][j] = a[i-1][j-1] + a[i-1][j];
      }
   }
   for (int i = 0; i <10 ; i++) {
      for (int j = 0; j <=i ; j++) {
         System.out.print(a[i][j]+"\t");
      }
      System.out.println();
   }
    }
}

(7) 第一个人10岁，第2个比第1个人大2岁，依次递推，请用递归方式计算出第8个人多大

public class MyClass {
    static int findAge(int i) {
        int age = 0;
        if (i == 1) {
            age = 10;
        } else {
            age = findAge(i - 1) + 2;
        }
        return age;
    }
    public static void main(String[] args) throws java.lang.Exception {
        System.out.print(findAge(8));
    }
}

(8) 冒泡排序

public class MyClass {
    public static void main(String[] args)  {
        int[] a = { 1, 5, 9, 7, 8, 6, 1, 3, 2, 4, 8 };

        for (int i = 0; i < (a.length - 1); i++) {
            for (int j = 0; j < (a.length - 1 - i); j++) {
                if (a[j] > a[j + 1]) {
                    int temp = a[j + 1];
                    a[j + 1] = a[j];
                    a[j] = temp;
                }
            }
        }

        for (int x = 0; x < a.length; x++) {
            System.out.print(a[x]+"\t");
        }
    }
}

(9) 快速排序

public class MyClass {
    static void f(int[] a, int start, int end) {
        if (start < end) {
            int left = start;
            int right = end;
            int temp = a[start];

            while (left < right) {
                while ((left < right) && (a[right] > temp)) {
                    right--;
                }

                if (left < right) {
                    a[left] = a[right];
                    left++;
                }

                while ((left < right) && (a[left] <= temp)) {
                    left++;
                }

                a[right] = a[left];
            }

            a[left] = temp;
            f(a, start, left);
            f(a, right + 1, end);
        }
    }

    public static void main(String[] args) throws java.lang.Exception {
        int[] a = { 12, 64, 58, 79, 310, 21, 98, 416, 351, 54 };
        f(a, 0, a.length - 1);

        for (int d : a) {
            System.out.print("\t" + d);
        }
    }
}

(10) 递归二分查找

public class MyClass {
      static int find(int[] i, int key, int low, int high) {
        int middle = (low + high) / 2;

        if (i[middle] > key) {
            return find(i, key, low, middle - 1);
        } else if (key > i[middle]) {
            return find(i, key, middle + 1, high);
        } else {
            return middle;
        }
    }

    public static void main(String[] args) throws java.lang.Exception {
        int[] a = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20 };
        System.out.println(find(a, 4, 0, a.length));
    }
}

(11) 十进制转二进制，并且计算1有多少位

public class Main {
   static void find(int x) {
        int result = 0;
        String sum = "";

        do {
            result = x % 2;
            sum = result + sum;
            x = x / 2;
        } while (x != 0);

        System.out.println(sum);

        String sum1 = sum.replaceAll("1", "");
        System.out.println("1的位数：" + (sum.length() - sum1.length()));
    }

    public static void main(String[] args) {
        find(9);
    }
}

(12) 一只青蛙一次可以跳上1级台阶，也可以跳上2级。求该青蛙跳上一个n级的台阶总共有多少种跳法

public class Main {
    static int JumpFloor(int target) {
        if (target == 1) {
            return 1;
        }

        if (target == 2) {
            return 2;
        }

        int first = 1;
        int second = 2;
        int sum = 0;

        for (int i = 2; i < target; i++) {
            sum = first + second;
            first = second;
            second = sum;
        }

        return sum;
    }
    public static void main(String[] args) {
        System.out.println(JumpFloor(5));
    }
}

（13）版本号比较

import java.io.*;
class test  
{
	public static void main (String[] args) throws java.lang.Exception
	{
		String a="1.20.1.3";
		String b="1.20.10.3";
		String[] c=a.split("\\.");
		String[] d=b.split("\\.");
		
		if(c.length>d.length){
		    for(int i=0;i<d.length;i++){
		        if(Integer.parseInt(c[i])>Integer.parseInt(d[i])){
		            System.out.print("最新："+a);
		            break;
		        }else{
		            System.out.print("最新："+b);
		            break;
		        }
		    }
		}else{
		        for(int i=0;i<c.length;i++){
		        if(Integer.parseInt(c[i])>Integer.parseInt(d[i])){
		            System.out.print("最新："+a);
		            break;
		        }else{
		            System.out.print("最新："+b);
		            break;
		        }
		    }
		    }
	}
}

(14)、正反三角

import java.io.*;
class test  
{
 public static void main (String[] args) throws java.lang.Exception
 {
     int n=6;
    
    for(int i=1;i<=n;i++){
            for(int j=n; i<=j; j--)
                System.out.print(" ");
            for(int j=1; j<=i; j++)
                System.out.print(i);
               
            System.out.println();
        }
        
        for(int i=n-1;i>=1;i--){
            for(int j=n; i<=j; j--)
                System.out.print(" ");
            for(int j=1; j<=i; j++)
                System.out.print(i);
               
            System.out.println();
        }
 }
}

(15)、棋盘矩形问题

import java.io.*;
class test  
{
	public static void main (String[] args) throws java.lang.Exception
	{
	    //规模  长 宽
	    int n=1;
        int m=3;

        //矩形个数：
        int rectangle=(m*(m+1)/2)*(n*(n+1)/2);
        
        //正方形个数
        if(n<m) {
            //这里交换顺序，以便后面的for遍历最小
            int temp=n;
            n=m;
            m=temp;
        }
        int square=m*n;
        for(int i=1;i<=m;i++)
            square+=(m-i)*(n-i);
            
        System.out.println("矩形个数:"+rectangle);
        System.out.print("正方形个数："+square+","+"长方形个数："+(rectangle-square));
	}
}

(16)选择排序

import java.io.*;
class test  
{
	public static void main (String[] args) throws java.lang.Exception
	{
		int[] a={156,79,8,6,3,1,6,5,7,94,15,21,6,5};
		for(int i=0;i<a.length;i++){
		    int min=i;
		    for(int j=i+1;j<a.length;j++){
		    if(a[j]<a[min]){
		        min=j;
		    }
		    }
		    if(i!=min){
		        int tmp=a[i];
		        a[i]=a[min];
		        a[min]=tmp;
		    }
		}
	 
	   for(int b:a){
	       System.out.print("\t"+b);
	   }
	}
}

(17)