Add elements of two arrays into a new array
Given two arrays of positive integers, add their elements into a new array. The solution should add both arrays, one by one starting from the 0th index, and split the sum into individual digits if it is a 2–digit number.
For example,
Input:
a = { 23, 5, 2, 7, 87 }
b = { 4, 67, 2, 8 }
Output: { 2, 7, 7, 2, 4, 1, 5, 8, 7 }
Input:
a = {}
b = { 4, 67, 2, 8 }
Output: { 4, 6, 7, 2, 8 }
a = { 23, 5, 2, 7, 87 }
b = { 4, 67, 2, 8 }
Output: { 2, 7, 7, 2, 4, 1, 5, 8, 7 }
Input:
a = {}
b = { 4, 67, 2, 8 }
Output: { 4, 6, 7, 2, 8 }
The idea is to run a loop that considers every pair of elements present at the same index in both arrays and adds them. If the sum is a 2–digit number, add its digits to the result array; otherwise, add the single-digit sum to the result array. Finally, add the remaining elements of the larger array to the result array.
Following is the C++, Java, and Python program that demonstrates it:
C++
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#include <iostream> #include <vector> using namespace std; // Recursive function to separate the digits of a positive integer // and add them to a given vector void split_number(int num, vector<int> &result) { if (num > 0) { split_number(num/10, result); result.push_back(num % 10); } } // Function to add two arrays void add(vector<int> const &a, vector<int> const &b, vector<int> &result) { int m = a.size(), n = b.size(); // loop till either `a` or `b` runs out int i = 0; while (i < m && i < n) { // get the sum of the next element from each array int sum = a[i] + b[i]; // separate the digits of the sum and add them to the output vector split_number(sum, result); i++; } // process remaining elements of the first vector, if any while (i < m) { split_number(a[i++], result); } // process remaining elements of the second vector, if any while (i < n) { split_number(b[i++], result); } } int main() { // input vectors vector<int> a = { 23, 5, 2, 7, 87 }; vector<int> b = { 4, 67, 2, 8 }; // vector to store the output vector<int> result; add(a, b, result); // print the output vector for (int i: result) { cout << i << " "; } return 0; } |
Output:
2 7 7 2 4 1 5 8 7
Java
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import java.util.ArrayList; import java.util.List; class Main { // Recursive function to separate the digits of a positive integer // and add them to a given list public static void split_number(int num, List<Integer> result) { if (num > 0) { split_number(num/10, result); result.add(num % 10); } } // Function to add two arrays public static void add(int[] a, int[] b, List<Integer> result) { int m = a.length, n = b.length; // loop till either `a` or `b` runs out int i = 0; while (i < m && i < n) { // get the sum of the next element from each array int sum = a[i] + b[i]; // separate the digits of the sum and add them to the output list split_number(sum, result); i++; } // process remaining elements of the first list, if any while (i < m) { split_number(a[i++], result); } // process remaining elements of the second list, if any while (i < n) { split_number(b[i++], result); } } public static void main(String[] args) { // input lists int[] a = { 23, 5, 2, 7, 87 }; int[] b = { 4, 67, 2, 8 }; // list to store the output List<Integer> result = new ArrayList<>(); add(a, b, result); // print the output list System.out.print(result); } } |
Output:
[2, 7, 7, 2, 4, 1, 5, 8, 7]
Python
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# Recursive function to separate the digits of a positive integer # and add them to a given list def split_number(num, result): if num > 0: split_number(num // 10, result) result.append(num % 10) # Function to add two lists def append(a, b, result): m = len(a) n = len(b) # loop till either `a` or `b` runs out i = 0 while i < m and i < n: # get the sum of the next element from each list total = a[i] + b[i] # separate the digits of the sum and add them to the output list split_number(total, result) i = i + 1 # process remaining elements of the first list, if any while i < m: split_number(a[i], result) i = i + 1 # process remaining elements of the second list, if any while i < n: split_number(b[i], result) i = i + 1 if __name__ == '__main__': # input lists a = [23, 5, 2, 7, 87] b = [4, 67, 2, 8] # list to store the output result = [] append(a, b, result) # print the output list print(result) |
Output:
[2, 7, 7, 2, 4, 1, 5, 8, 7]
Here’s another solution that constructs a string containing the result by appending the sum of each pair of elements to it and finally add each character to a list of integers.
C++
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#include <iostream> #include <vector> #include <algorithm> using namespace std; // Function to add two arrays void add(vector<int> const &a, vector<int> const &b, vector<int> &result) { int m = a.size(), n = b.size(); string str; // loop till either `a` or `b` runs out int i = 0; while (i < m && i < n) { str += to_string(a[i] + b[i]); i++; } // process remaining elements of the first vector, if any while (i < m) { str += to_string(a[i++]); } // process remaining elements of the second vector, if any while (i < n) { str += to_string(b[i++]); } // add characters of the output string to a given vector of integers for (char c: str) { result.push_back(c - '0'); } } int main() { // input vectors vector<int> a = { }; vector<int> b = { 4, 67, 2, 8 }; // vector to store the output vector<int> result; add(a, b, result); // print the output vector for (int i: result) { cout << i << " "; } return 0; } |
Output:
4 6 7 2 8
Java
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import java.util.ArrayList; import java.util.List; class Main { // Function to add two arrays public static void add(int[] a, int[] b, List<Integer> result) { int m = a.length, n = b.length; String str = ""; // loop till either `a` or `b` runs out int i = 0; while (i < m && i < n) { str += (a[i] + b[i]); i++; } // process remaining elements of the first list, if any while (i < m) { str += (a[i++]); } // process remaining elements of the second list, if any while (i < n) { str += (b[i++]); } // add characters of the output string to a given list of integers char[] chars = str.toCharArray(); for (char c: chars) { result.add(c - '0'); } } public static void main(String[] args) { // input lists int[] a = { }; int[] b = { 4, 67, 2, 8 }; // list to store the output List<Integer> result = new ArrayList<>(); add(a, b, result); // print the output list System.out.print(result); } } |
Output:
[4, 6, 7, 2, 8]
Python
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# Function to add two lists def add(a, b): m = len(a) n = len(b) s = '' # loop till either `a` or `b` runs out i = 0 while i < m and i < n: s += str(a[i] + b[i]) i = i + 1 # process remaining elements of the first list, if any while i < m: s = s + str(a[i]) i = i + 1 # process remaining elements of the second list, if any while i < n: s = s + str(b[i]) i = i + 1 # add characters of the output string to a given list of integers return [int(c) for c in s] if __name__ == '__main__': # input lists a = [] b = [4, 67, 2, 8] # list to store the output result = add(a, b) # print the output list print(result) |
Output:
[4, 6, 7, 2, 8]
The time complexity of both above-discussed methods is O(m + n) and runs in constant space. Here, m and n are the size of the first and second array, respectively.
Author: Aditya Goel
Thanks for reading.
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