字符串的字典序最大子字符串

给定一个字符串s 我们必须找到一个字符串的字典序最大子字符串

例子：

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

Input : s = "asdfaa"
Output : sdfaa

这个想法很简单，我们遍历所有子字符串。对于每个子字符串，我们将其与当前结果进行比较，并在需要时更新结果。

下面是实现：

C++

// CPP program to find the lexicographically
// maximum substring.
#include 
using namespace std;
 
string LexicographicalMaxString(string str)
{
    // loop to find the max lexicographic
    // 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;
}

Java

// Java program to find the lexicographically
// maximum substring.
 
class GFG {
 
    static String LexicographicalMaxString(String str)
    {
        // loop to find the max lexicographic
        // 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

Python3

# Python 3 program to find the
# lexicographically maximum substring.
def LexicographicalMaxString(str):
     
    # loop to find the max lexicographic
    # 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

C#

// C# program to find the lexicographically
// maximum substring.
 
using System;
public class GFG {
 
    static String LexicographicalMaxString(String str)
    {
        // loop to find the max lexicographic
        // 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

Javascript

 
// JavaScript program to find the lexicographically
// maximum substring.
   function LexicographicalMaxString(str)
    {
        // loop to find the max lexicographic
    // substring in the substring array
    var mx = "";
    for (var i = 0; i < str.length; ++i) {
        if (mx.localeCompare(str.substring(i)) <= 0) {
            mx = str.substring(i);
        }
    }
 
    return mx;
}
 
// Driver code
   var str = "ababaa";
   document.write(LexicographicalMaxString(str));
 
// This code is contributed by 29AjayKumar
 

输出：

babaa

优化 ：
我们找到最大的字符及其所有索引。现在我们简单地遍历最大字符的所有实例来找到字典上最大的子字符串。

这里我们按照上面的方法。

C++

// C++ program to find the lexicographically
// maximum substring.
#include 
using namespace std;
 
string LexicographicalMaxString(string str)
{
    char maxchar = 'a';
    vector 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;
}

Java

// Java program to find the lexicographically
// maximum substring.
import java.io.*;
import java.util.*;
class GFG
{   
  static String LexicographicalMaxString(String str)
  {
    char maxchar = 'a';
    ArrayList index = new ArrayList();
 
    // We store all the indexes of maximum
    // characters we have in the string
    for (int i = 0; i < str.length(); i++)
    {
      if (str.charAt(i) >= maxchar)
      {
        maxchar = str.charAt(i);
        index.add(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.substring(index.get(i),
                        str.length()).compareTo( maxstring) > 0)
      {
        maxstring = str.substring(index.get(i),
                                  str.length());
      }
    }
    return maxstring;
  }
 
  // Driver code
  public static void main (String[] args)
  {   
    String str = "acbacbc";  
    System.out.println(LexicographicalMaxString(str));
  }
}
 
// This code is contributed by rag2127.

Python3

# 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

C＃

// C# program to find the lexicographically
// maximum substring.
using System;
using System.Collections.Generic;
 
class GFG{
     
static string LexicographicalMaxString(string str)
{
    char maxchar = 'a';
    List index = new List();
     
    // 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.Add(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.Count; i++)
    {
        if (str.Substring(index[i]).CompareTo(maxstring) > 0)
        {
            maxstring = str.Substring(index[i]);
        }
    }
    return maxstring;
}
 
// Driver code
static public void Main()
{
    string str = "acbacbc";
     
    Console.Write(LexicographicalMaxString(str));
}
}
 
// This code is contributed by avanitrachhadiya2155

Javascript

// Javascript program to find the lexicographically
// maximum substring.
 
function LexicographicalMaxString(str)
{
    let maxchar = 'a';
    let index = [];
     
    // We store all the indexes of maximum
    // characters we have in the string
    for (let i = 0; i < str.length; i++)
    {
      if (str[i] >= maxchar)
      {
        maxchar = str[i];
        index.push(i);
      }
    }
    let maxstring = "";
  
    // We form a substring from that maximum
    // character index till end and check if
    // its greater that maxstring
    for (let i = 0; i < index.length; i++)
    {
      if (str.substring(index[i],
                        str.length) > maxstring)
      {
        maxstring = str.substring(index[i],
                                  str.length);
      }
    }
    return maxstring;
}
 
// Driver code
let str = "acbacbc"; 
document.write(LexicographicalMaxString(str));
 
// This code is contributed by ab2127

输出：

cbc