Greatest number that can be formed from a pair in a given Array

Given an array arr[], the task is to find the largest number that can be formed from a pair in the given array.

Examples:

Input: arr[] = { 3, 1, 9, 2 }
Output: 93
The pair (3, 9) leads to forming of maximum number 93

Input: arr[] = { 23, 14, 16, 25, 3, 9 }
Output: 2523
The pair (23, 25) leads to forming of maximum number 2523

Recommended: Please try your approach on {IDE} first, before moving on to the solution.

Approach: The idea is to form every possible pairs of the array. Then for each pair X and Y, join them as XY and YX and take the maximum out of all such pairs.

for every possible in array (X, Y) $ans = max(ans, XY, YX)$

Below is the implementation of the above approach:

C++

// C++ implementation to find the 
// greatest number from the 
// given pairs of the array 
  
#include <bits/stdc++.h> 
using namespace std; 
  
// Function to find the greatest 
// number formed from the pairs 
string getNumber(int a, int b) 
{ 
    string X = to_string(a); 
    string Y = to_string(b); 
  
    // first append Y at 
    // the end of X 
    string XY = X + Y; 
  
    // then append X at 
    // the end of Y 
    string YX = Y + X; 
  
    // Now see which of the 
    // two formed numbers 
    // is greater than other 
    return XY > YX ? XY : YX; 
} 
  
// Function to find pairs from array 
void printMaxPair(int arr[], int n) 
{ 
    int largest = INT_MIN; 
  
    // Iterate through all pairs 
    for (int i = 0; i < n; i++) 
        for (int j = i + 1; j < n; j++) { 
            int number = stoi( 
                getNumber(arr[i], arr[j])); 
            largest = max(largest, number); 
        } 
    cout << largest; 
} 
  
// Driver code 
int main() 
{ 
    int a[] = { 23, 14, 16, 25, 3, 9 }; 
    int n = sizeof(a) / sizeof(a[0]); 
    printMaxPair(a, n); 
    return 0; 
} 

Java

// Java implementation to find the 
// greatest number from the 
// given pairs of the array 
import java.util.*; 
  
class GFG{ 
  
// Function to find the greatest 
// number formed from the pairs 
static String getNumber(int a, int b) 
{ 
    String X = Integer.toString(a); 
    String Y = Integer.toString(b); 
  
    // First append Y at 
    // the end of X 
    String XY = X + Y; 
  
    // Then append X at 
    // the end of Y 
    String YX = Y + X; 
  
    // Now see which of the 
    // two formed numbers 
    // is greater than other 
    return XY.compareTo(YX) > 0 ? XY : YX; 
      
} 
  
// Function to find pairs from array 
static void printMaxPair(int arr[], int n) 
{ 
    int largest = Integer.MIN_VALUE; 
  
    // Iterate through all pairs 
    for(int i = 0; i < n; i++) 
       for(int j = i + 1; j < n; j++) 
       { 
          int number = Integer.parseInt(getNumber(arr[i], 
                                                  arr[j])); 
          largest = Math.max(largest, number); 
       } 
       System.out.println(largest); 
} 
  
// Driver code 
public static void main(String[] args) 
{ 
    int a[] = { 23, 14, 16, 25, 3, 9 }; 
    int n = a.length; 
      
    printMaxPair(a, n); 
} 
} 
  
// This code is contributed by offbeat 

Python3

# Python3 implementation to find the 
# greatest number from the 
# given pairs of the array 
import sys; 
  
# Function to find the greatest 
# number formed from the pairs 
def getNumber(a, b): 
  
    X = str(a); 
    Y = str(b); 
  
    # first append Y at 
    # the end of X 
    XY = X + Y; 
  
    # then append X at 
    # the end of Y 
    YX = Y + X; 
  
    # Now see which of the 
    # two formed numbers 
    # is greater than other 
    if(XY > YX): 
        return XY; 
    else:  
        return YX; 
  
# Function to find pairs from array 
def printMaxPair(arr, n): 
  
    largest = -sys.maxsize - 1; 
  
    # Iterate through all pairs 
    for i in range(0, n): 
        for j in range(i + 1, n): 
            number = int(getNumber(arr[i],  
                                   arr[j])); 
            largest = max(largest, number); 
          
    print(largest); 
  
# Driver code 
a = [ 23, 14, 16, 25, 3, 9 ]; 
n = len(a); 
printMaxPair(a, n); 
  
# This code is contributed by Code_Mech 

C#

// C# implementation to find the 
// greatest number from the 
// given pairs of the array 
using System; 
  
class GFG{ 
  
// Function to find the greatest 
// number formed from the pairs 
static String getNumber(int a, int b) 
{ 
    String X = a.ToString(); 
    String Y = b.ToString(); 
  
    // First append Y at 
    // the end of X 
    String XY = X + Y; 
  
    // Then append X at 
    // the end of Y 
    String YX = Y + X; 
  
    // Now see which of the 
    // two formed numbers 
    // is greater than other 
    return XY.CompareTo(YX) > 0 ? XY : YX; 
      
} 
  
// Function to find pairs from array 
static void printMaxPair(int []arr, int n) 
{ 
    int largest = int.MinValue; 
  
    // Iterate through all pairs 
    for(int i = 0; i < n; i++) 
       for(int j = i + 1; j < n; j++) 
       { 
          int number = Int32.Parse(getNumber(arr[i], 
                                             arr[j])); 
          largest = Math.Max(largest, number); 
       } 
       Console.WriteLine(largest); 
} 
  
// Driver code 
public static void Main(String[] args) 
{ 
    int []a = { 23, 14, 16, 25, 3, 9 }; 
    int n = a.Length; 
      
    printMaxPair(a, n); 
} 
} 
  
// This code is contributed by Amit Katiyar 

Output:

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My Personal Notes

Recommended: Please try your approach on {IDE} first, before moving on to the solution.

C++

Java

Python3

C#

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