Remove a number from a string

Question

I have to print this in the console:

9 7 5 3 1

7 5 3 1

5 3 1

3 1

1

My current code is:

  String seq = "9 7 5 3 1";
  Scanner nums = new Scanner(seq);

  int count = 5;
  while (count > 1){

  int firstNum = nums.nextInt();
  int secNum = nums.nextInt();

     if(firstNum > secNum ){
        //I'm trying to remove the first number in each iteration of the sequence.
        seq = seq.remove(firstNum);
        count --;
        System.out.println(seq);
     }
 }

How would I remove the first number each time? I don't want to write a bunch of loops for each condition.

Do you have to start with a `String`? If so, `seq = seq.substring(2);` should work in the loop. Just keep printing `seq`. — Elliott Frisch, May 18 '20 at 15:40
@Schred True. But it's a `String`. Which is why I asked the first question in my comment. — Elliott Frisch, May 18 '20 at 15:42
Does this answer your question? [how can I use the for loop in java to print out the word chicken in a triangle shape?](https://stackoverflow.com/questions/33089334/how-can-i-use-the-for-loop-in-java-to-print-out-the-word-chicken-in-a-triangle-s) — Arvind Kumar Avinash, Jun 23 '20 at 10:12

Harshal Parekh · Answer 1 · 2020-05-18T16:08:08.930

You should work with numbers, not strings.

int start = 9;
while (start >= 1) {
    int temp = start;
    while (temp > 0) {
        System.out.print(temp + " ");
        temp -= 2;
    }
    start -= 2;
    System.out.println();
}

In your code:

seq = seq.remove(firstNum);

String does not have a remove method that takes an int.

If you want to remove a number from the sequence, consider storing the numbers in a data structure like an ArrayList that has a remove method.

List<Integer> list = new ArrayList<>(Arrays.asList(9, 7 ,5, 3, 1));
int n = list.size();

for (int i = 0; i < n; i++) {
    System.out.println(list);
    list.remove(0);
}

Note: Do not do this

for (int i = 0; i < list.size(); i++)

If your condition is on list.size() and you remove in the loop, then the list size is changed while iterating and the loop will run n / 2 times only.

Check this answer to safely remove elements from a list.

cegredev · Answer 2 · 2020-05-18T16:07:47.590

1

Change your if-statement to this:

if (firstNum > secNum ){ 
    count --;
    System.out.println(seq);

    // This means "Assign seq the value of everything after the next space (" ")
    seq = seq.substring(seq.indexOf(" ") + 1);
}

edited May 18 '20 at 16:07

answered May 18 '20 at 15:45

cegredev

1,485
2
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25

user · Answer 3 · 2020-05-18T16:00:16.870

As Harshal Parekh said, you should use numbers. You can do this

for (int i = 9; i --> 1;) {
    for (int j = i; j --> 1;) System.out.print(j + " ");
    System.out.println();
}

You can also use recursion to avoid that extra space at the end of the line:

public void printLine(int from) {
  if (from == 1) {
    System.out.println(1);
    return;
  }
  System.out.print(from + " ");
  printLine(from - 2);
}

Which you could use like this:

for (int i = 9; i --> 1;) printLine(i);

Or like this:

printLines(9);
//if you define this method, that is
public void printLines(int from) {
  printLine(from);
  printLines(from - 2);
}

score 1 · Answer 4 · answered May 18 '20 at 15:59

1

Another approach :

  //code to get input in string
  String seq = "9 7 5 3 1";
  while (seq.length() >1){
         int index= seq.indexOf(" ")>0? seq.indexOf(" ")+1: 0 ;
         seq = seq.substring(index);
         System.out.println(seq);
    }
  }

answered May 18 '20 at 15:59

Hemant

1,403
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Arvind Kumar Avinash · Answer 5 · 2020-05-18T16:37:45.543

Make sure you use nums.hasNextInt() before nums.nextInt() to avoid java.util.NoSuchElementException.

String does not have remove method. You can make use of substring(int beginIndex) to remove the part of the string before the index, beginIndex.

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        String seq = "9 7 5 3 1";
        Scanner nums = new Scanner(seq);

        int count = 5;
        while (count > 1 && nums.hasNextInt()) {
            int firstNum = nums.nextInt();
            int secNum = 0;
            if (nums.hasNextInt()) {
                secNum = nums.nextInt();
            }
            if (firstNum > secNum) {
                System.out.println(seq);
                seq = seq.substring(seq.indexOf(' ', seq.indexOf(' ') + 1) + 1);
                count--;
            }
        }
    }
}

Output:

9 7 5 3 1
5 3 1
1

Note: String has two overloaded methods with the name, indexOf and the solution uses both of them.

Remove a number from a string

5 Answers5