package day1;
import java.util.Arrays;
import java.util.HashMap;
import java.util.Map;
public class demo1 {
public static void main(String[] args) {
int[] nums={11,15,2,7};
int target=9;
int[] ints = t1(nums, target);
//暴力法
System.out.println(Arrays.toString(ints));
//哈希表法
System.out.println(Arrays.toString(t2(nums,target)));
}
public static int[] t1(int[] nums,int target){
for (int i = 0; i < nums.length; i++) {
for (int j = i+1; j < nums.length; j++) {
if (nums[i]+nums[j]==target){
return new int[]{i,j};
}
}
}
return null;
}
public static int[] t2(int[]nums,int target){
HashMap map = new HashMap<>();
for (int i = 0; i < nums.length; i++) {
//将值作为key，下标作为值
map.put(nums[i],i);
}
for (int i = 0; i < nums.length; i++) {
//求出差
int tem=target-nums[i];
//map.containsKey判断是否存在这个key
if (map.containsKey(tem)&&map.get(tem)!=i){
return new int[]{i,map.get(tem)};
}
}
return null;
}
}
结果：[外链图片转存失败,源站可能有防盗链机制,建议将图片保存下来直接上传(img-VU4k8UDd-1652607948873)(C:Userszwf12AppDataRoamingTyporatypora-user-imagesimage-20220515172804818.png)]
数组 1.杨辉三角
public class demo02 {
public static void main(String[] args) {
//1声明并初始化二维数组
int[][] yangHui=new int[10][];
//2给数组的元素赋值
for (int i=0;i
yangHui[i]=new int[i+1];
//2.1给首末元素赋值
yangHui[i][0]=yangHui[i][i]=1;
//给每行的非首末元素赋值
if(i>1){
for (int j = 1; j < yangHui[i].length-1; j++) {
yangHui[i][j]=yangHui[i-1][j-1]+yangHui[i-1][j];
}
}
}
//3遍历二维数组
for (int i = 0; i < yangHui.length; i++) {
for (int j = 0; j < yangHui[i].length; j++) {
System.out.print(yangHui[i][j]+" ");
}
System.out.println();
}
}
}
结果：[外链图片转存失败,源站可能有防盗链机制,建议将图片保存下来直接上传(img-s7gdUxWF-1652607948874)(C:Userszwf12AppDataRoamingTyporatypora-user-imagesimage-20220514193607483.png)]
2.创建一个长度为6的int型数组，要求取值为1-30，同时元素值各不相同package FileInPutStreamTest;
import java.util.Arrays;
public class demo04 {
public static void main(String[] args) {
//1.为数组分配6个空间
int[] arr=new int[6];
//2.元素赋值
for (int i = 0; i < arr.length; i++) {
arr[i]=(int)((Math.random()*30)+1);
for (int j=0;j
if (arr[j]==arr[i]){
i--;
break;
}
}
}
//3.遍历数组
for(int a:arr){
System.out.print(a+"t");
}
}
}
加强一点点的版本
public class demo03 {
public static void main(String[] args) {
int[] ints = get(5);
for (int a:ints){
System.out.print(a+"t");
}
System.out.println();
System.out.println("最大值"+getMax(ints));
}
//最大值
public static Integer getMax(int[] arr){
int max=arr[0];
for (int i = 1; i < arr.length; i++) {
if (max
max=arr[i];
}
}
return max;
}
//随机生成1-100的5个随机数,不能重复，返回数组
public static int[] get(int sun){
//新建动态数组，sun要生成的随机数的个数
int[] arr = new int[sun];
for (int i = 0; i
arr[i]=(int) (Math.random()*(100-1)+1);
for (int j = 0; j < i; j++) {
if (arr[i]==arr[j]){
i--;
break;
}
}
}
return arr;
}
}
结果：
[外链图片转存失败,源站可能有防盗链机制,建议将图片保存下来直接上传(img-nw6xd2el-1652607948875)(C:Userszwf12AppDataRoamingTyporatypora-user-imagesimage-20220515172616329.png)]
3.数组的复制，反转，线性查找package demoOne;
public class demo01 {
public static void main(String[] args) {
String[] arr=new String[]{"JJ","DD","MM","GG","AA"};
//====复制=====
//1.新建一个相同长度的数组
String[] arr1 = new String[arr.length];
//2.循环赋值
for (int i=0;i
arr1[i]=arr[i];
}
//遍历数组arr1
System.out.println("arr1:");
for (String a:arr1){
System.out.print(a+"t");
}
//====反转===== 将刚刚复制的值反转arr1
for (int i=0,j=arr1.length-1;i
String temp=arr1[i];
arr1[i]=arr1[j];
arr1[j]=temp;
}
System.out.println();
//遍历数组arr1
System.out.println("反转后的arr1:");
for (String a:arr1){
System.out.print(a+"t");
}
System.out.println();
//====线性查找=====
//要查找的值
String dest="AA";
System.out.println("从arr中，要找的元素"+dest);
boolean isFlag=true;
for (int i=0;i< arr.length;i++){
if (dest.equals(arr[i])){
System.out.println("找到了指定的元素是第"+(i+1)+"个");
isFlag=false;
break;
}
}
if (isFlag){
System.out.println("没有找到");
}
}
}
结果：
[外链图片转存失败,源站可能有防盗链机制,建议将图片保存下来直接上传(img-bNI9mQBk-1652607948876)(C:Userszwf12AppDataRoamingTyporatypora-user-imagesimage-20220515172456653.png)]
4.二分法查找- 二分查找的数必须有序
package demoOne;
public class demo02 {
public static void main(String[] args) {
//1.创建数组
int[] ints = get(5);
//2.排序
int[] by = getBY(ints);
//3.删除该数组
System.out.println("排序后的数组");
getAll(by);
//输入要查找的值
int test=by[3];
System.out.println();
System.out.println("要查找的值"+test);
//首元素下标
int head=0;
//尾元素下标
int end=by.length-1;
while (head<=end){
//中间下标
int dest=(head+end)/2;
if (by[dest]==test){
System.out.println("找到了该元素在第"+(dest+1)+"个");
break;
}
if (by[dest]
head=dest+1;
}
if (by[dest]>test){
end=dest-1;
}
}
}
//随机生成1-100的sun个随机数,不能重复，返回数组
public static int[] get(int sun){
//新建动态数组，sun要生成的随机数的个数
int[] arr = new int[sun];
for (int i = 0; i
arr[i]=(int) (Math.random()*(100-1)+1);
for (int j = 0; j < i; j++) {
if (arr[i]==arr[j]){
i--;
break;
}
}
}
return arr;
}
//打印数组
public static void getAll(int[] arr){
for (int a:arr){
System.out.print(a+"t");
}
}
//升序排序
public static int[] getBY(int[] arr){
for (int i=0;i
for (int j = i+1; j
if (arr[i]>arr[j]){
int temp=arr[i];
arr[i]=arr[j];
arr[j]=temp;
}
}
}
return arr;
}
//倒序排序
public static int[] getBYDesc(int[] arr){
for (int i=0;i
for (int j = i+1; j
if (arr[i]
int temp=arr[i];
arr[i]=arr[j];
arr[j]=temp;
}
}
}
return arr;
}
}
结果：[外链图片转存失败,源站可能有防盗链机制,建议将图片保存下来直接上传(img-DaGpny0c-1652607948877)(C:Userszwf12AppDataRoamingTyporatypora-user-imagesimage-20220515172418482.png)]
