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Java Exercises: Given two non-negative integers represented as string, return their sum

Java Basic: Exercise-189 with Solution

Write a Java program to given two non-negative integers num1 and num2 represented as string, return the sum of num1 and num2.

Pictorial Presentation:

Java Basic Exercises: Given two non-negative integers represented as string, return their sum

Sample Solution:

Java Code:

import java.util.*;
public class Solution {
 public static void main(String[] args) {
  String n1 = "123";
  String n2 = "456";
  System.out.println("'" + n1 + "'" + " + " + "'" + n2 + "'" + " = " + addStrings(n1, n2));
 }
 public static String addStrings(String n1, String n2) {
  int[] x = str_num(n1);
  int[] y = str_num(n2);
  int[] sum = new int[Math.max(x.length, y.length) + 1];
  int z = 0;
  int index = sum.length - 1;
  int i = 0;
  int j = 0;
  while (index >= 0) {
   if (i < x.length) {
    z += x[i++];
   }
   if (j < y.length) {
    z += y[j++];
   }
   sum[index--] = z % 10;
   z /= 10;
  }
  StringBuilder sb = new StringBuilder(sum.length);
  for (i = (sum[0] == 0 ? 1 : 0); i < sum.length; ++i) {
   sb.append(sum[i]);
  }
  return sb.toString();
 }

 private static int[] str_num(String num) {
  char[] digits = num.toCharArray();
  int[] number = new int[digits.length];
  int index = number.length - 1;
  for (char digit: digits) {
   number[index--] = digit - '0';
  }
  return number;
 }
}

Sample Output:

'123' + '456' = 579

Flowchart:

Flowchart: Java exercises: Given two non-negative integers represented as string, return their sum

Java Code Editor:

Company:  Google Airbnb

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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",         // "[1234]"
    "0001234a",      // "[1234a]"
    "101234",        // "[101234]"
    "000002829839",  // "[2829839]"
    "0",             // "[0]"
    "0000000",       // "[0]"
    "0000009",       // "[9]"
    "000000z",       // "[z]"
    "000000.z",      // "[.z]"
};
for (String s : in) {
    System.out.println("[" + s.replaceFirst("^0+(?!$)", "") + "]");
}

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