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Find the Substring with maximum product

  • Difficulty Level : Easy
  • Last Updated : 18 Nov, 2021

Given string str containing only lowercase English alphabets of size N, the task is to find the substring having the maximum product. 
 

Each English alphabet has a value such that val(‘a’) = 0, val(‘b’) = 1, val(‘c’) = 2, ……, val(‘z’) = 25.

Examples: 
 

Input: str = “sdtfakdhdahdzz” 
Output: hdzz 
Here, the maximum product is for the substring “hdzz”. 
product = 7 * 3 * 25 * 25 = 13125
Input: str = “geeksforgeeks” 
Output: geeksforgeeks 
 

 

Approach: 
 

  • First, traverse through the given string while maintaining a maximum product value.
  • Product will always keep increasing or will remain constant unless we encounter an ‘a’. Hence, start a new substring after each ‘a’ occurrence.
  • Also, along with the maximum product value, we will also maintain the substring to which the maximum product corresponds.
  • Once the entire string has been traversed, print the substring corresponding to the maximum product.

Below is the implementation of the above approach: 
 

C++




// C++ program to find the maximum product substring
 
#include <bits/stdc++.h>
using namespace std;
 
// Function to return the value of a character
int value(char x)
{
    return (int)(x - 'a');
}
 
// Function to find the maximum product substring
string maximumProduct(string str, int n)
{
    // To store substrings
    string answer = "", curr = "";
    long long maxProduct = 0, product = 1;
 
    for (int i = 0; i < n; i++) {
        product *= 1LL * value(str[i]);
 
        curr += str[i];
 
        // Check if current product is maximum
        // possible or not
        if (product >= maxProduct) {
            maxProduct = product;
            answer = curr;
        }
 
        // If product is 0
        if (product == 0) {
            product = 1;
            curr = "";
        }
    }
 
    // Return the substring with maximum product
    return answer;
}
 
// Driver code
int main()
{
    string str = "sdtfakdhdahdzz";
 
    int n = str.size();
 
    // Function call
    cout << maximumProduct(str, n) << endl;
 
    return 0;
}

Java




// Java program to find the maximum product subString
 
class GFG{
  
// Function to return the value of a character
static int value(char x)
{
    return (int)(x - 'a');
}
  
// Function to find the maximum product subString
static String maximumProduct(String str, int n)
{
    // To store subStrings
    String answer = "", curr = "";
    long maxProduct = 0, product = 1;
  
    for (int i = 0; i < n; i++) {
        product *= 1L * value(str.charAt(i));
  
        curr += str.charAt(i);
  
        // Check if current product is maximum
        // possible or not
        if (product >= maxProduct) {
            maxProduct = product;
            answer = curr;
        }
  
        // If product is 0
        if (product == 0) {
            product = 1;
            curr = "";
        }
    }
  
    // Return the subString with maximum product
    return answer;
}
  
// Driver code
public static void main(String[] args)
{
    String str = "sdtfakdhdahdzz";
  
    int n = str.length();
  
    // Function call
    System.out.print(maximumProduct(str, n) +"\n");
  
}
}
 
// This code is contributed by 29AjayKumar

Python3




# Python3 program to find the maximum product sub
 
# Function to return the value of a character
def value(x):
    return (ord(x) - ord('a'))
 
# Function to find the maximum product sub
def maximumProduct(strr, n):
 
    # To store subs
    answer = ""
    curr = ""
    maxProduct = 0
    product = 1
 
    for i in range(n):
        product *=value(strr[i])
 
        curr += strr[i]
 
        # Check if current product is maximum
        # possible or not
        if (product >= maxProduct):
            maxProduct = product
            answer = curr
 
        # If product is 0
        if (product == 0):
            product = 1
            curr = ""
 
    # Return the sub with maximum product
    return answer
 
# Driver code
if __name__ == '__main__':
    strr = "sdtfakdhdahdzz"
 
    n = len(strr)
 
    # Function call
    print(maximumProduct(strr, n))
 
# This code is contributed by mohit kumar 29

C#




// C# program to find the maximum product subString
 
using System;
 
public class GFG{
 
// Function to return the value of a character
static int value(char x)
{
    return (int)(x - 'a');
}
 
// Function to find the maximum product subString
static String maximumProduct(String str, int n)
{
    // To store subStrings
    String answer = "", curr = "";
    long maxProduct = 0, product = 1;
 
    for (int i = 0; i < n; i++) {
        product *= 1L * value(str[i]);
 
        curr += str[i];
 
        // Check if current product is maximum
        // possible or not
        if (product >= maxProduct) {
            maxProduct = product;
            answer = curr;
        }
 
        // If product is 0
        if (product == 0) {
            product = 1;
            curr = "";
        }
    }
 
    // Return the subString with maximum product
    return answer;
}
 
// Driver code
public static void Main(String[] args)
{
    String str = "sdtfakdhdahdzz";
 
    int n = str.Length;
 
    // Function call
    Console.Write(maximumProduct(str, n) +"\n");
 
}
}
// This code is contributed by PrinciRaj1992

Javascript




<script>
// Javascript program to find the
// maximum product subString
 
// Function to return the value of a character
function value(x)
{
    return (x.charCodeAt() - 'a'.charCodeAt());
}
    
// Function to find the maximum product subString
function maximumProduct(str, n)
{
    // To store subStrings
    let answer = "", curr = "";
    let maxProduct = 0, product = 1;
    
    for (let i = 0; i < n; i++) {
        product *= (1 * value(str[i]));
    
        curr += str[i];
    
        // Check if current product is maximum
        // possible or not
        if (product >= maxProduct) {
            maxProduct = product;
            answer = curr;
        }
    
        // If product is 0
        if (product == 0) {
            product = 1;
            curr = "";
        }
    }
    
    // Return the subString with maximum product
    return answer;
}
    
 
// Driver Code
 
     let str = "sdtfakdhdahdzz";
    
    let n = str.length;
    
    // Function call
    document.write(maximumProduct(str, n) +"<br/>");
     
</script>
Output: 
hdzz

 

Time Complexity: O(N)

Auxiliary Space: O(1)


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