Lexicographical Maximum substring of string

Given a string s we have to find the lexicographical maximum substring of a string
Examples: 

Input : s = "ababaa"
Output : babaa
Explanation : "babaa" is the maximum lexicographic susbtring formed from this string

Input : s = "asdfaa"
Output : sdfaa

The idea is simple, we traverse through all substrings. For every substring, we compare it with the current result and update the result if needed.
Below is the implementation:
 

C++

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// CPP program to find the lexicographically
// maximum substring.
#include <bits/stdc++.h>
using namespace std;
 
string LexicographicalMaxString(string str)
{
    // loop to find the max leicographic
    // substring in the substring array
    string mx = "";
    for (int i = 0; i < str.length(); ++i)
        mx = max(mx, str.substr(i));
 
    return mx;
}
 
// Driver code
int main()
{
    string str = "ababaa";
    cout << LexicographicalMaxString(str);
    return 0;
}

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Java

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// Java program to find the lexicographically
// maximum substring.
 
class GFG {
 
    static String LexicographicalMaxString(String str)
    {
        // loop to find the max leicographic
        // substring in the substring array
        String mx = "";
        for (int i = 0; i < str.length(); ++i) {
            if (mx.compareTo(str.substring(i)) <= 0) {
                mx = str.substring(i);
            }
        }
 
        return mx;
    }
 
    // Driver code
    public static void main(String[] args)
    {
        String str = "ababaa";
        System.out.println(LexicographicalMaxString(str));
    }
}
// This code is contributed by 29AjayKumar

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Python3

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# Python 3 program to find the
# lexicographically maximum substring.
def LexicographicalMaxString(str):
     
    # loop to find the max leicographic
    # substring in the substring array
    mx = ""
    for i in range(len(str)):
        mx = max(mx, str[i:])
 
    return mx
 
# Driver code
if __name__ == '__main__':
    str = "ababaa"
    print(LexicographicalMaxString(str))
     
# This code is contributed by
# Sanjit_Prasad

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C#

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// C# program to find the lexicographically
// maximum substring.
 
using System;
public class GFG {
 
    static String LexicographicalMaxString(String str)
    {
        // loop to find the max leicographic
        // substring in the substring array
        String mx = "";
        for (int i = 0; i < str.Length; ++i) {
            if (mx.CompareTo(str.Substring(i)) <= 0) {
                mx = str.Substring(i);
            }
        }
 
        return mx;
    }
 
    // Driver code
    public static void Main()
    {
        String str = "ababaa";
        Console.WriteLine(LexicographicalMaxString(str));
    }
}
 
// This code is contributed by 29AjayKumar

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Output: 

babaa


 

Optimization : 
We find the largest character and all its indexes. Now we simply traverse through all instances of the largest character to find lexicographically maximum substring.
Here we follow the above approach. 
 

C++

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// C# program to find the lexicographically
// maximum substring.
#include <bits/stdc++.h>
using namespace std;
 
string LexicographicalMaxString(string str)
{
    char maxchar = 'a';
    vector<int> index;
 
    // We store all the indexes of maximum
    // characters we have in the string
    for (int i = 0; i < str.length(); i++) {
        if (str[i] >= maxchar) {
            maxchar = str[i];
            index.push_back(i);
        }
    }
    string maxstring = "";
 
    // We form a substring from that maximum
    // character index till end and check if
    // its greater that maxstring
    for (int i = 0; i < index.size(); i++) {
        if (str.substr(index[i], str.length()) > maxstring) {
            maxstring = str.substr(index[i], str.length());
        }
    }
    return maxstring;
}
 
// Driver code
int main()
{
    string str = "acbacbc";
    cout << LexicographicalMaxString(str);
    return 0;
}

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Python3

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# Python 3 program to find
# the lexicographically
# maximum substring.
def LexicographicalMaxString(st):
 
    maxchar = 'a'
    index = []
 
    # We store all the indexes
    # of maximum characters we
    # have in the string
    for i in range(len(st)):
        if (st[i] >= maxchar):
            maxchar = st[i]
            index.append(i)
 
    maxstring = ""
 
    # We form a substring from that
    # maximum character index till
    # end and check if its greater
    # that maxstring
    for i in range(len(index)):
        if (st[index[i]: len(st)] >
            maxstring):
            maxstring = st[index[i]:
                        len(st)]
    return maxstring
 
# Driver code
if __name__ == "__main__":
 
    st = "acbacbc"
    print(LexicographicalMaxString(st))
 
# This code is contributed by Chitranayal

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Output: 

cbc


 

https://youtu.be/pMS4P7wxTU8
 

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