字符串的子字符串

查找具有N个字符的字符串的非空子字符串的总数。在这里，我们使用“适当”一词，因为我们不将字符串本身视为输出的一部分。

Input : str = “abc”
Output : 6
Proper substrings are “a”, “b”, “c”, “ab”, “bc”, “abc”

Input : str = “abcd”
Output : 10
Proper substrings are “a”, “b”, “c”, “d”, “ab”, “bc”, “cd”, “abc”, “bcd” and “abcd”

非空子字符串的计数为n *(n + 1)/ 2

如果我们也将空字符串作为子字符串包括在内，则计数变为n *(n + 1)/ 2 + 1

以上公式如何运作?

1. 长度为1的子字符串数为n (我们可以选择n个字符的任何一个)
2. 长度为2的子串的数量为n-1 (我们可以选择相邻的n-1个对中的任何一个)
3. 长度为三的子串的数量为n-2
   (我们可以选择相邻的n-2个三元组中的任何一个)
4. 通常，长度为k的子串的成员为n-k + 1 ，其中1 <= k <= n

从1到n的所有长度的子字符串的总数=
n +(n-1)+(n-2)+(n-3)+…2 + 1
= n *(n + 1)/ 2

C++

// CPP program to count number of substrings
// of a string
#include 
using namespace std;
  
int countNonEmptySubstr(string str)
{
   int n = str.length();
   return n*(n+1)/2;
}
  
// driver code
int main()
{
    string s = "abcde";
    cout << countNonEmptySubstr(s);
    return 0;
}

Java

// Java program to count number of substrings
// of a string
import java.io.*;
  
public class GFG {
      
    static int countNonEmptySubstr(String str)
    {
        int n = str.length();
        return n * (n + 1) / 2;
    }
      
    // Driver code
    public static void main(String args[])
    {
        String s = "abcde";
        System.out.println(
                  countNonEmptySubstr(s));
    }
}
  
// This code is contributed 
// by Manish Shaw (manishshaw1)

Python3

# Python3 program to count number
# of substrings of a string
  
def countNonEmptySubstr(str):
    n = len(str);
    return int(n * (n + 1) / 2);
  
# driver code
s = "abcde";
print (countNonEmptySubstr(s));
  
# This code is contributed by
# Manish Shaw (manishshaw1)

C#

// C# program to count number 
// of substrings of a string
using System;
class GFG {
      
    static int countNonEmptySubstr(string str)
    {
        int n = str.Length;
        return n * (n + 1) / 2;
    }
      
    // Driver Code
    public static void Main()
    {
        string s = "abcde";
        Console.Write(countNonEmptySubstr(s));
    }
}
  
// This code is contributed 
// by Manish Shaw (manishshaw1)

输出：

15