【JAVA练习题15】【数字与字符串】字符串STRING详解

dlnb526 · 发表于 2020-3-22 11:04:20

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【JAVA练习题】【索引贴】
https://fishc.com.cn/thread-157183-1-1.html

习题来源：how2j
本贴下答案内容为我和广大鱼油解答以及提示哦！答案仅供参考！如果大神们有更好的做法还请不吝指教。

【JAVA练习题15】【数字与字符串】字符串STRING详解

1.随机字符串

创建一个长度是5的随机字符串，随机字符有可能是数字，大写字母或者小写字母

给点提示: 数字和字符之间可以通过互相转换

char c = 'A';
short s = (short) c;

复制代码

通过这个手段就能够知道字符 a-z A-Z 0-9 所对应的数字的区间了

需要用到ASCII码对照表

2.字符串数组排序
创建一个长度是8的字符串数组
使用8个长度是5的随机字符串初始化这个数组
对这个数组进行排序，按照每个字符串的首字母排序(无视大小写)

注1：不能使用Arrays.sort() 要自己写
注2：无视大小写，即 Axxxx 和 axxxxx 没有先后顺序

3.穷举法破解密码

1. 生成一个长度是3的随机字符串，把这个字符串作为当做密码

2. 使用穷举法生成长度是3个字符串，匹配上述生成的密码

要求：分别使用多层for循环和递归解决上述问题

参考解答：

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评个分呗！

永远的渣滓 · 发表于 2020-3-22 18:51:09

wuhao4221961 · 发表于 2020-3-23 09:08:18

慢慢来最快

放屁蹦出屎 · 发表于 2020-3-23 09:16:16

这个习题不错

璀璨·狸 · 发表于 2020-4-1 08:39:17

谢谢楼主

璀璨·狸 · 发表于 2020-4-1 08:46:38

观摩大佬

bailean · 发表于 2020-4-1 11:25:10

学到啦

majian890324 · 发表于 2020-4-30 20:42:26

不错不错，支持一下~~~

情缘丶夜未央 · 发表于 2020-7-22 12:17:55

YIDASun · 发表于 2020-7-23 16:40:48

我写一个第一题的答案，随机生成字符串的答案。
写的不算好，很多地方比较复杂，比如将类型多次转换，判定条件复杂等等，但能作为一个参考。

package first.test.Demo;
public class RandomString {
public static void main(String[] args) throws Exception {
//生成需要判断的数字，对应字符A-Z 0-9
String targetNum[] = new String[] {"48","49","50","51","52","53","54","55","56","57"};
String targetLetter[] = new String[] {"65","66","67","68","69","70","71","72","73","74","75","76","77","78","79","80","81","82","83","84","85","86","87","88","89","90"};
int i = 1;
String temp = "";
while (i <= 5) {
String number = String.valueOf((int) (Math.random()*100));
if (isIn(number, targetNum)) { //如果为数字，转为0-9
int number_int = Integer.valueOf(number);
char c = (char) number_int;
temp += c;
i += 1;
} else if (isIn(number, targetLetter)) { //判断是否为字母
if (((int) (Math.random()*100)) % 2 == 1) { //用随机数判断，如果为奇数则为小写字母
int number_int = Integer.valueOf(number) + 32;
char c = (char) number_int;
temp += c;
i += 1;
} else {
int number_int = Integer.valueOf(number);
char c = (char) number_int;
temp += c;
i += 1;
}
} else {
continue;
}
}
System.out.println(temp);
}
//判断生成数是否在目标数组中
private static boolean isIn(String substring, String[] source) {
for (int i = 0; i < source.length; i++) {
String aSource = source[i];
if (aSource.equals(substring)) {
return true;
}
}
return false;
}
}

复制代码

YIDASun · 发表于 2020-7-23 16:46:00

本帖最后由 YIDASun 于 2020-7-23 16:48 编辑

测试结果，运气好可以有大小写和数字

YIDASun · 发表于 2020-7-24 15:36:20

今天补充第二题答案。
首先，将昨天的类RandomString稍作修改，方法main()返回目标字符串：

package first.test.Demo;
public class RandomString {
public String main() throws Exception {
//生成需要判断的数字，对应字符A-Z 0-9
String targetNum[] = new String[] {"48","49","50","51","52","53","54","55","56","57"};
String targetLetter[] = new String[] {"65","66","67","68","69","70","71","72","73","74","75","76","77","78","79","80","81","82","83","84","85","86","87","88","89","90"};
int i = 1;
String temp = "";
while (i <= 5) {
String number = String.valueOf((int) (Math.random()*100));
if (isIn(number, targetNum)) { //如果为数字，转为0-9
int number_int = Integer.valueOf(number);
char c = (char) number_int;
temp += c;
i += 1;
} else if (isIn(number, targetLetter)) { //判断是否为字母
if (((int) (Math.random()*100)) % 2 == 1) { //用随机数判断，如果为奇数则为小写字母
int number_int = Integer.valueOf(number) + 32;
char c = (char) number_int;
temp += c;
i += 1;
} else {
int number_int = Integer.valueOf(number);
char c = (char) number_int;
temp += c;
i += 1;
}
} else {
continue;
}
}
return temp;
}
//判断生成数是否在目标数组中
private static boolean isIn(String substring, String[] source) {
for (int i = 0; i < source.length; i++) {
String aSource = source[i];
if (aSource.equals(substring)) {
return true;
}
}
return false;
}
}

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然后创建类StringRank，用RandomString生成目标数组，再用冒泡法排序：

package first.test.Demo;
public class StringRank {
public static void main(String[] args) throws Exception {
String initialArray[] = new String[8];
System.out.print("初始化数组为：");
for (int i = 0; i < 8; i++) {
initialArray[i] = new RandomString().main();
System.out.print(initialArray[i]);
System.out.print(" ");
}
System.out.println();
//冒泡排序，从小到大
for (int m = (initialArray.length - 1); m > 0; m--) {
for (int n = 0; n < m; n++) {
int tempA = (int) initialArray[n].charAt(0);
int tempB = (int) initialArray[n+1].charAt(0);
//将小写字母的值减去32，就不区分大小写了
if (tempA > 96) {
tempA -= 32;
}
if (tempB > 96) {
tempB -= 32;
}
if (tempA > tempB) {
String temp = initialArray[n];
initialArray[n] = initialArray[n+1];
initialArray[n+1] = temp ;
}
}
}
System.out.print("排序后的数组为：");
for (int i = 0; i < 8; i++) {
System.out.print(initialArray[i]);
System.out.print(" ");
}
System.out.println();
}
}

复制代码

可以看一下运行结果：

YIDASun · 发表于 2020-7-24 16:34:39

害，干脆再写写第三题答案，用for循环实现：

package first.test.Demo;
public class ForLoop {
public static void main(String[] args) throws Exception {
String password = new RandomString().main();
System.out.println(password);
String targetList[] = new String[] {"0","1","2","3","4","5","6","7","8","9","a","b","c","d","e","f","g","h","i","j","k","l","m","n","o","p","q","r","s","t","u","v","w","x","y","z","A","B","C","D","E","F","G","H","I","J","K","L","M","N","O","P","Q","R","S","T","U","V","W","X","Y","Z"};
String temp = "";
for (int i1 = 0; i1 < targetList.length; i1++) {
for (int i2 = 0; i2 < targetList.length; i2++) {
for (int i3 = 0; i3 < targetList.length; i3++) {
for (int i4 = 0; i4 < targetList.length; i4++) {
for (int i5 = 0; i5 < targetList.length; i5++) {
temp = targetList[i1] + targetList[i2] + targetList[i3] + targetList[i4] + targetList[i5];
if (password.equals(temp)) {
System.out.println("i1 = " + i1);
System.out.println("i2 = " + i2);
System.out.println("i3 = " + i3);
System.out.println("i4 = " + i4);
System.out.println("i5 = " + i5);
break;
}
}
if (password.equals(temp)) {
break;
}
}
if (password.equals(temp)) {
break;
}
}
if (password.equals(temp)) {
break;
}
}
if (password.equals(temp)) {
break;
}
}
System.out.println("找到目标密码为：" + temp);
}
}

复制代码

这里用break终止循环，因为每次只能终止一个for，所以要终止5回。
因为字符串长度我设置为5，所以有点慢，小心电脑卡死。
可以看看效果：

YIDASun · 发表于 2020-7-24 16:41:22

上面的代码还能写成一个return返回的方法，一个return就能终结所有for循环，可以尝试一下。

递归的就不写了，哈哈哈哈哈哈。

小曲sy · 发表于 2020-7-28 14:13:00

lsez2014 · 发表于 2021-5-2 19:11:05

875041187 · 发表于 2022-4-24 15:29:55

谢谢楼主分享

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测试结果，运气好可以有大小写和数字

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