Java面试题冲刺第二十天--算法(1)

select num,count(num) from T group by num order by count(num) desc; 

package com.softsec.demo;
import java.util.HashMap;
import java.util.Map;
import java.util.Random;

public class getRepeat {
	
	public static void cyclingDemo ( int[] arr){
		for (int x = 0; x < 10; x++) {
			int sumber1 = 0;
			for (int j = 0; j < 20; j++) {
				//数组中的数循环比较
				if (x == arr[j]) {
					sumber1++;
				} else {
					continue;
				}
			}
			System.out.println(x + " -- 重复个数:" + sumber1);
		}
	}
	public static void main (String[] args){
		Random random = new Random();
		int[] arr = new int[20];
		for (int i = 0; i < 20; i++) {
			arr[i] = random.nextInt(10);
			if (i < arr.length - 1) {
				System.out.print(arr[i]+"，");
			} else {
				System.out.print(arr[i] + "\r\n 结果：" + "\r\n" );
			}
		}
		// 输出arr数组中重复元素，重复数量
		// 循环处理
		cyclingDemo(arr);
		// map处理
		// mapDemo(arr);
	}

package com.softsec.demo;
import java.util.HashMap;
import java.util.Map;
import java.util.Random;

public class getRepeat {
	
	public static void mapDemo ( int[] arr){
		//将数据转成集合
		Map<Integer, Integer> map = new HashMap();
		for (int a = 0; a < arr.length; a++) {
			if (map.get(arr[a])!=null){
				map.put(arr[a],map.get(arr[a])+1);
			}
			else {
				map.put(arr[a],1);
			}
		}
		for (int i = 0; i <10 ; i++) {
			System.out.println(i + " -- 重复个数：" + map.get(i));
		}
	}
}

	public static void main (String[] args){
		Random random = new Random();
		int[] arr = new int[20];
		for (int i = 0; i < 20; i++) {
			arr[i] = random.nextInt(10);
			if (i < arr.length - 1) {
				System.out.print(arr[i]+"，");
			} else {
				System.out.print(arr[i] + "\r\n 结果：" + "\r\n" );
			}
		}
		// 输出arr数组中重复元素，重复数量
		// 循环处理
		// cyclingDemo(arr);
		// map处理
		mapDemo(arr);
	}
}

package com.softsec.demo;

public class BinaryQry {
	public static void main(String[] args) {
		// TODO Auto-generated method stub
		int[] arr = new int[] { 1, 20, 23, 24, 35, 46, 77, 78, 99, 100 };
		int index = search(arr,0,arr.length-1,78);
		//int index = search2(arr, 11);
		if (index == -1) {
			System.out.println("没找到");
			return;
		}
		System.out.println("在数组的第" + (index+1) + "位");
	}
	
	public static int search(int[] arr, int left, int right, int key) {
		if (left <= right) {
			int mid = (left + right) / 2;
			if (key < arr[mid]) {
				return search(arr, left, mid - 1, key);
			} else if (key > arr[mid]) {
				return search(arr, mid + 1, right, key);
			} else {
				return mid;
			}
		}
		return -1;
	}
	
	public static int search2(int[] arr, int key) {
		int left = 0;
		int right = arr.length - 1;
		int mid = 0;
		while (left <= right) {
			mid = (left + right) / 2;
			if (key == arr[mid]) {
				return mid;
			} else if (key > arr[mid]) {
				left = mid + 1;
			} else if (key < arr[mid]) {
				right = mid - 1;
			}
		}
		return -1;
	}
}

package com.softsec.demo;

public class ArrayMerge {
	
	public static int[] mergeArray(int arrayM[],int arrayN[]){
		int newArray[];
		// 定义一个新数组，长度为两个有序数组长度之和
		newArray = new int[arrayM.length + arrayN.length];
		// start:arrayM数组下标    end：arrayN数组下标  k：newArray新数组下标
		int start=0,end=0,k=0;
		// 循环比较两个数组，较小元素的放入新数组，较小元素所在数组下标加一，较大元素对应的数组下标不加一，直到某一个下标等于数组长度时退出循环
		while(start<arrayM.length && end<arrayN.length) {
			if(arrayM[start] <= arrayN[end]) {
				newArray[k++] = arrayM[start++];
			}else{
				newArray[k++] = arrayN[end++];
			}
		}
		
		while(start < arrayM.length) {
			newArray[k++] = arrayM[start++];
		}
		while(end < arrayN.length) {
			newArray[k++] = arrayN[end++];
		}
		return newArray;
	}
	
	public static void print(int[] arr) {
		for(int i=0; i<arr.length;i++) {
			if (i < arr.length -1) {
				System.out.print(arr[i]+"，");
			} else {
				System.out.print(arr[i]);
			}
		}
	}
	public static void main(String[] args) {
		int[] arrayM = {1,3,5,7,8,9,14,16,21};
		int[] arrayN = {0,10,20,30,40,50};
		print(mergeArray(arrayM,arrayN));
	}
}