﻿ Java: Sum all values from all subsets by n natural numbers

# Java Exercises: Sum of all the elements from all possible subsets of a set formed by first n natural numbers

## Java Basic: Exercise-193 with Solution

Write a Java program that accept an integer and find the sum of all the elements from all possible subsets of a set formed by first n natural numbers.

Sample Solution:

Java Code:

``````import java.util.Scanner;
public class Solution {
public static void main(String[] args) {
Scanner in = new Scanner(System.in);
System.out.print("Input a positive integer: ");
int n = in .nextInt();
int result = (n * (n + 1) / 2) * (1 << (n - 1));
System.out.print("Sum of subsets of n is : " + result);
}
}
```
```

Sample Output:

```Input a positive integer:  25
Sum of subsets of n is : 1157627904
```

Flowchart: Java Code Editor:

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## Java: Tips of the Day

How to remove leading zeros from alphanumeric text?

Regex is the best tool for the job; what it should be depends on the problem specification. The following removes leading zeroes, but leaves one if necessary (i.e. it wouldn't just turn "0" to a blank string).

```s.replaceFirst("^0+(?!\$)", "")
```

The ^ anchor will make sure that the 0+ being matched is at the beginning of the input. The (?!\$) negative lookahead ensures that not the entire string will be matched.

Test harness:

```String[] in = {
"01234",         // ""
"0001234a",      // "[1234a]"
"101234",        // ""
"000002829839",  // ""
"0",             // ""
"0000000",       // ""
"0000009",       // ""
"000000z",       // "[z]"
"000000.z",      // "[.z]"
};
for (String s : in) {
System.out.println("[" + s.replaceFirst("^0+(?!\$)", "") + "]");
}```

Ref: https://bit.ly/2Qdcl8a