﻿ Java: Two non-negative integers as string, return their sum

# 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: 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 ? 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: 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