第1题：打印九九乘法表
/*
1*1=1
2*1=2 2*2=4
3*1=3 3*2=6 3*3=9
4*1=4 4*2=8 4*3=12 4*4=16
5*1=5 5*2=10 5*3=15 5*4=20 5*5=25
6*1=6 6*2=12 6*3=18 6*4=24 6*5=30 6*6=36
7*1=7 7*2=14 7*3=21 7*4=28 7*5=35 7*6=42 7*7=49
8*1=8 8*2=16 8*3=24 8*4=32 8*5=40 8*6=48 8*7=56 8*8=64
9*1=9 9*2=18 9*3=27 9*4=36 9*5=45 9*6=54 9*7=63 9*8=72 9*9=81
*/
public class ArrayDemo00 {
public static void main(String[] args) {
for (int i = 1; i <= 9 ; i++) {
for (int j = 1; j <= i ; j++) {
System.out.print(i + "*" + j + "=" + i*j + "\t");
}
System.out.println();
}
}
}
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第2题：冒泡排序
import java.util.Arrays;
public class ArrayDemo01 {
// 冒泡排序
public static void main(String[] args) {
int[] arr = {30,29,18,40,33};
boolean falg = false;
for (int i = 0; i < arr.length; i++) {
flag = true;
for (int j = 0; j < arr.length-1-i; j++) {
if (arr[j] > arr[j+1]){
int t = arr[j];
arr[j] = arr[j+1];
arr[j+1] = t;
flag = false;
}
}
if (flag){
break;
}
}
System.out.println(Arrays.toString(arr));
}
}
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第3题：二分查找
public class ArrayDemo05 {
public static void main(String[] args) {
int[] array = {10,20,30,40,50,60,70};
int ele = 40;
System.out.println(getIndexByEle(array,ele));
}
public static int getIndexByEle(int[] arr,int ele){
int minIndex=0;
int maxIndex=arr.length-1;
int cenIndex=(minIndex+maxIndex)/2;
while (minIndex <= maxIndex){
if (ele == arr[cenIndex]){
return cenIndex;
} else if(ele > arr[cenIndex]){
minIndex = cenIndex + 1;
} else if(ele < arr[cenIndex]){
maxIndex = cenIndex - 1;
}
cenIndex = (minIndex+maxIndex)/2;
}
return -1;
}
}
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第4题：求素数
public class SuShu {
public static void main(String[] args) {
boolean flag;
int m = 100;
for(int i = 2; i < m;i++){
flag=true;
for (int j = 2; j <= Math.sqrt(i); j++) {
if (i%j == 0){
flag = false;
break;
}
}
if (flag == true){
System.out.println(i + " ");
}
}
}
}
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第5题：合并两个有序数组
import java.util.Arrays;
// 合并两个有序数组
public class Demo03 {
public static void main(String[] args) {
int[] arr1 = {1,2,3,6};
int[] arr2 = {5,7,8,9};
System.out.println(Arrays.toString(merge(arr1,arr2)));
}
static int[] merge(int[] arr1, int[] arr2){
int x = 0;
int y = 0;
int z = 0;
int[] result = new int[arr1.length + arr2.length];
while (x<arr1.length&&y<arr2.length){
if (arr1[x] <= arr2[y]){
result[z] = arr1[x];
x++;
} else {
result[z] = arr2[y];
y++;
}
z++;
}
// 判断哪一个数组被遍历到尾部，则此处将另一个数组添加到汇总数组中即可；
// 此时 i=x，并i++,将M数组中剩余值添加到result中；
if (x != arr1.length){
for (int i = x; i < arr1.length; i++) {
result[z] = arr1[i];
z++;
}
}else {
for (int i = y; i < arr2.length; i++) {
result[z] = arr2[i];
z++;
}
}
return result;
}
}
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第6题：输入12345，按位输出1-2-3-4-5
import java.util.Scanner;
public class Demo02 {
public static void main(String[] args) {
Scanner scanner = new Scanner(System.in);
System.out.println("请输入正整数：");
int num = scanner.nextInt();
rePrint(num);
}
static void rePrint(int num){
if (num > 9){
rePrint( num / 10);
}
System.out.println(num % 10 + " ");
}
}
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第7题：数组反转
import java.util.Arrays;
// 数组反转
public class ArrayDemo03 {
public static void main(String[] args) {
int[] arr = {10,20,30,40,50,60};
System.out.println(Arrays.toString(reArray(arr)));
}
public static int[] reArray(int[] arrays){
int[] result = new int[arrays.length];
for (int i = 0,j=result.length-1; i < arrays.length; i++,j--) {
result[j] = arrays[i];
}
return result;
}
}
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第8题：链表反转
public class Solution {
public ListNode ReverseList(ListNode head) {
ListNode p = new ListNode(0);
p.next = null;
while(head != null){
ListNode tmp = head.next;
head.next = p.next;
p.next = head;
head = tmp;
}
return p.next;
}
}
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第9题：统计一个字符串中数字出现的个数
public class Que2 {
public static void main(String[] args) {
String s = "123004533";
char[] array = s.toCharArray();
int[] count = new int[10]; // 存放个数
for (int i = 48; i < 58; i++) {
int a = 0;
for (int j = 0; j < array.length; j++) {
if (array[j] == i){
a++;
}
}
count[i-48] = a;
}
for (int i = 0; i < count.length; i++) {
System.out.println(i + "的个数是："+count[i]);
}
}
}
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第10题：字符串压缩
public class Solution3 {
public static void main(String[] args) {
String str = "aaabcdworr";
System.out.println(compressString(str));;
}
static String compressString(String S) {
if (S.length() == 0) { // 空串处理
return S;
}
StringBuffer ans = new StringBuffer();
int cnt = 1;
char ch = S.charAt(0);
for (int i = 1; i < S.length(); ++i) {
if (ch == S.charAt(i)) {
cnt++;
} else {
ans.append(ch);
ans.append(cnt);
ch = S.charAt(i);
cnt = 1;
}
}
ans.append(ch);
ans.append(cnt);
if (ans.length() >= S.length()){
return S;
} else {
return ans.toString();
}
// return ans.length() >= S.length() ? S : ans.toString();
}
}
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第11题：判断两个字符串是否是旋转词
public class Rotation {
public boolean chkRotation(String A, int lena, String B, int lenb) {
// write code here
if(lena!=lenb)
return false;
String AA = A + A;
return AA.contains(B);
}
//测试
public static void main(String[] args) {
String text = "PVNMCXZNZBETCM";
String pattern = "CNTZXMNZEBMVCd";
Rotation rotation = new Rotation();
System.out.println(rotation.chkRotation(text,text.length(),pattern,pattern.length()));
}
}
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