Write one to nine summation algorithm using JAVA

Write one to nine summation algorithm using JAVA

Find the 123456789 string 1..9 without changing the number position random +- requires the expression result to sum to 100, write such an expression

package demo;

import java.util.HashSet;
import java.util.Random;
import java.util.Set;
import java.util.regex.Pattern;

/**
* @author yeqv
* @program A2
* @Classname a3
* @Date 2022/1/13 17:17
* @Email w16638771062@163.com
*/
public class a3 {
public static void main (String[] args) {
//define a collection
Set set = new HashSet();
int index = 0 ;
while ( true ) {
//Define an array of character type
String[] s1 = { "" , "+" , "-" };
//Instantiate a random generator object
Random rand = new Random();
//Instantiate a constructor object of a string type with the first string "1"
StringBuilder sbu = new StringBuilder( "1" );
//Define a loop, the maximum number is 9
for ( int i = 2 ; i <= 9 ; i++) {
//Insert a random string from the array s1 into the string constructor "sbu"
sbu.append(s1[rand.nextInt(s1.length)]);
//Insert the number i of the current loop into the constructor
sbu.append(i);
}
//Use regular expressions to formulate a format, each paragraph starts with +- or empty, followed by numbers between 0-9, for example
// 12+345-6+78-9
var p3 = Pattern.compile( "[+-]*[0-9]+" );
//match the string inside the string constructor with the format
var m3 = p3.matcher(sbu);
//Set a variable of type int as the sum of the formula
int sum = 0 ;
//Check whether the strings in the constructor match the format in order
while (m3.find()) {
//Convert subsequence string to int type assignment and num
int num = Integer.parseInt(m3.group());
sum += num;
}
//Determine whether the sum of the expression is 100 and the string sbu cannot be included in the set
if (sum == 100 && !set.contains(sbu.toString())) {
// output sequence and formula
System.out.printf( "%d, %s = 100%n" , ++index, sbu);
//Add the string to the collection set
}
//Judging that the number of strings in the collection is enough to end with 10
if (set.size() == 10 ) {
break ;
}
}

}

}

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