Square of large number represented as String
Given a very large number, the task is to write a program to compute its square.
Examples:
Input: 9999
Output: 99980001
9999*9999 = 99980001
Input: 45454545
Output: 2066115661157025
45454545*45454545 = 2066115661157025
Naive Approach: A naive approach is to calculate the squares my multiplying the number with itself. But in C++, if the input is a large number, the resultant square will overflow.
Efficient Approach: An efficient approach is to store the number as strings, and perform multiplication of two large numbers.
Below is the implementation of the above approach:
C++
// C++ program to multiply two numbers // represented as strings. #include <bits/stdc++.h> using namespace std; // Multiplies str1 and str2, and prints result. string multiply(string num1, string num2) { int n1 = num1.size(); int n2 = num2.size(); if (n1 == 0 || n2 == 0) return "0"; // will keep the result number in vector // in reverse order vector<int> result(n1 + n2, 0); // Below two indexes are used to find positions // in result. int i_n1 = 0; int i_n2 = 0; // Go from right to left in num1 for (int i = n1 - 1; i >= 0; i--) { int carry = 0; int n1 = num1[i] - '0'; // To shift position to left after every // multiplication of a digit in num2 i_n2 = 0; // Go from right to left in num2 for (int j = n2 - 1; j >= 0; j--) { // Take current digit of second number int n2 = num2[j] - '0'; // Multiply with current digit of first number // and add result to previously stored result // at current position. int sum = n1 * n2 + result[i_n1 + i_n2] + carry; // Carry for next iteration carry = sum / 10; // Store result result[i_n1 + i_n2] = sum % 10; i_n2++; } // store carry in next cell if (carry > 0) result[i_n1 + i_n2] += carry; // To shift position to left after every // multiplication of a digit in num1. i_n1++; } // ignore '0's from the right int i = result.size() - 1; while (i >= 0 && result[i] == 0) i--; // If all were '0's - means either both or // one of num1 or num2 were '0' if (i == -1) return "0"; // generate the result string string s = ""; while (i >= 0) s += std::to_string(result[i--]); return s; } // Driver code int main() { string str1 = "454545454545454545"; cout << multiply(str1, str1); return 0; } |
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Java
// Java program to multiply two numbers // represented as strings. class GFG { // Multiplies str1 and str2, and prints result. public static String multiply(String num1, String num2) { int n1 = num1.length(); int n2 = num2.length(); if (n1 == 0 || n2 == 0) return "0"; // will keep the result number in vector // in reverse order int[] result = new int[n1 + n2]; // Below two indexes are used to find positions // in result. int i_n1 = 0; int i_n2 = 0; // Go from right to left in num1 for (int i = n1 - 1; i >= 0; i--) { int carry = 0; int n_1 = num1.charAt(i) - '0'; // To shift position to left after every // multiplication of a digit in num2 i_n2 = 0; // Go from right to left in num2 for (int j = n2 - 1; j >= 0; j--) { // Take current digit of second number int n_2 = num2.charAt(j) - '0'; // Multiply with current digit of first number // and add result to previously stored result // at current position. int sum = n_1 * n_2 + result[i_n1 + i_n2] + carry; // Carry for next iteration carry = sum / 10; // Store result result[i_n1 + i_n2] = sum % 10; i_n2++; } // store carry in next cell if (carry > 0) result[i_n1 + i_n2] += carry; // To shift position to left after every // multiplication of a digit in num1. i_n1++; } // ignore '0's from the right int i = result.length - 1; while (i >= 0 && result[i] == 0) i--; // If all were '0's - means either both or // one of num1 or num2 were '0' if (i == -1) return "0"; // generate the result string String s = ""; while (i >= 0) s += Integer.toString(result[i--]); return s; } // Driver code public static void main(String[] args) { String str1 = "454545454545454545"; System.out.println(multiply(str1, str1)); } } // This code is contributed by // sanjeev2552 |
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C#
// C# program to multiply two numbers // represented as strings. using System; using System.Collections.Generic; class GFG { // Multiplies str1 and str2, // and prints result. public static String multiply(String num1, String num2) { int n1 = num1.Length; int n2 = num2.Length; if (n1 == 0 || n2 == 0) return "0"; // will keep the result number in vector // in reverse order int[] result = new int[n1 + n2]; // Below two indexes are used to // find positions in result. int i_n1 = 0; int i_n2 = 0; int i = 0; // Go from right to left in num1 for (i = n1 - 1; i >= 0; i--) { int carry = 0; int n_1 = num1[i] - '0'; // To shift position to left after every // multiplication of a digit in num2 i_n2 = 0; // Go from right to left in num2 for (int j = n2 - 1; j >= 0; j--) { // Take current digit of second number int n_2 = num2[j] - '0'; // Multiply with current digit of first number // and add result to previously stored result // at current position. int sum = n_1 * n_2 + result[i_n1 + i_n2] + carry; // Carry for next iteration carry = sum / 10; // Store result result[i_n1 + i_n2] = sum % 10; i_n2++; } // store carry in next cell if (carry > 0) result[i_n1 + i_n2] += carry; // To shift position to left after every // multiplication of a digit in num1. i_n1++; } // ignore '0's from the right i = result.Length - 1; while (i >= 0 && result[i] == 0) i--; // If all were '0's - means either both or // one of num1 or num2 were '0' if (i == -1) return "0"; // generate the result string String s = ""; while (i >= 0) s += (result[i--]).ToString(); return s; } // Driver code public static void Main(String[] args) { String str1 = "454545454545454545"; Console.WriteLine(multiply(str1, str1)); } } // This code is contributed by Princi Singh |
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Output:
206611570247933883884297520661157025
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