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📜  长度为K的子字符串的计数,具有精确的K个不同字符

📅  最后修改于: 2021-05-24 16:53:09             🧑  作者: Mango

给定一个小写字母的字符串str和一个整数K ,任务是计算长度为K的所有子串,这些子串恰好有K个不同的字符。

例子:

天真的方法:
这个想法是生成所有长度为K的子字符串,并为每个子字符串计数不同字符的数量。如果字符串的长度为N ,则可以有N – K + 1个长度为K的子字符串。生成这些子字符串将需要O(N)复杂度,而检查每个子字符串则需要O(K)复杂度,因此将总体复杂度设为O(N * K)。

高效的方法:
这个想法是使用窗口滑动技术。维护一个大小为K的窗口,并使用HashMap保留该窗口中所有字符的计数。遍历字符串减少HashMap中前一个窗口的第一个字符的计数,并增加当前窗口的最后一个字符的频率。如果在长度为K的窗口中不同字符的计数等于K ,则将答案增加1。

下面是上述方法的实现:

C++
// C++ program to find the 
// count of k length substrings 
// with k distinct characters 
// using sliding window 
#include  
using namespace std; 
  
// Function to return the 
// required count of substrings 
int countSubstrings(string str, int K) 
{ 
    int N = str.size(); 
    // Store the count 
    int answer = 0; 
  
    // Store the count of 
    // distinct characters 
    // in every window 
    unordered_map map; 
  
    // Store the frequency of 
    // the first K length substring 
    for (int i = 0; i < K; i++) { 
  
        // Increase frequency of 
        // i-th character 
        map[str[i]]++; 
    } 
  
    // If K distinct characters 
    // exist 
    if (map.size() == K) 
        answer++; 
  
    // Traverse the rest of the 
    // substring 
    for (int i = K; i < N; i++) { 
  
        // Increase the frequency 
        // of the last character 
        // of the current substring 
        map[str[i]]++; 
        // Decrease the frequency 
        // of the first character 
        // of the previous substring 
        map[str[i - K]]--; 
  
        // If the character is not present 
        // in the current substring 
        if (map[str[i - K]] == 0) { 
            map.erase(str[i - K]); 
        } 
  
        // If the count of distinct 
        // characters is 0 
        if (map.size() == K) { 
            answer++; 
        } 
    } 
  
    // Return the count 
    return answer; 
} 
  
// Driver code 
int main() 
{ 
    // string str 
    string str = "aabcdabbcdc"; 
  
    // integer K 
    int K = 3; 
  
    // Print the count of K length 
    // substrings with k distinct characters 
    cout << countSubstrings(str, K) << endl; 
  
    return 0; 
}


Java
// Java program to find the count 
// of k length substrings with k 
// distinct characters using 
// sliding window 
import java.util.*; 
  
class GFG{ 
  
// Function to return the 
// required count of substrings 
public static int countSubstrings(String str, 
                                int K) 
{ 
    int N = str.length(); 
      
    // Store the count 
    int answer = 0; 
  
    // Store the count of 
    // distinct characters 
    // in every window 
    Map map = new HashMap(); 
  
    // Store the frequency of 
    // the first K length substring 
    for(int i = 0; i < K; i++) 
    { 
          
        // Increase frequency of 
        // i-th character 
        if (map.get(str.charAt(i)) == null) 
        { 
            map.put(str.charAt(i), 1); 
        } 
        else
        { 
            map.put(str.charAt(i), 
            map.get(str.charAt(i)) + 1); 
        } 
    } 
  
    // If K distinct characters 
    // exist 
    if (map.size() == K) 
        answer++; 
  
    // Traverse the rest of the 
    // substring 
    for(int i = K; i < N; i++) 
    { 
  
        // Increase the frequency 
        // of the last character 
        // of the current substring 
        if (map.get(str.charAt(i)) == null) 
        { 
            map.put(str.charAt(i), 1); 
        } 
        else
        { 
            map.put(str.charAt(i), 
            map.get(str.charAt(i)) + 1); 
        } 
          
        // Decrease the frequency 
        // of the first character 
        // of the previous substring 
        map.put(str.charAt(i - K), 
        map.get(str.charAt(i - K)) - 1); 
  
        // If the character is not present 
        // in the current substring 
        if (map.get(str.charAt(i - K)) == 0) 
        { 
            map.remove(str.charAt(i - K)); 
        } 
  
        // If the count of distinct 
        // characters is 0 
        if (map.size() == K) 
        { 
            answer++; 
        } 
    } 
  
    // Return the count 
    return answer; 
} 
  
// Driver code 
public static void main(String[] args) 
{ 
      
    // string str 
    String str = "aabcdabbcdc"; 
  
    // integer K 
    int K = 3; 
  
    // Print the count of K length 
    // substrings with k distinct characters 
    System.out.println(countSubstrings(str, K)); 
} 
} 
  
// This code is contributed by grand_master


Python3
# Python3 program to find the 
# count of k length substrings 
# with k distinct characters 
# using sliding window 
  
# Function to return the 
# required count of substrings 
def countSubstrings(str, K): 
  
    N = len(str) 
  
    # Store the count 
    answer = 0
  
    # Store the count of 
    # distinct characters 
    # in every window 
    map = {} 
  
    # Store the frequency of 
    # the first K length substring 
    for i in range(K): 
  
        # Increase frequency of 
        # i-th character 
        map[str[i]] = map.get(str[i], 0) + 1
          
    # If K distinct characters 
    # exist 
    if (len(map) == K): 
        answer += 1
  
    # Traverse the rest of the 
    # substring 
    for i in range(K, N): 
  
        # Increase the frequency 
        # of the last character 
        # of the current substring 
        map[str[i]] = map.get(str[i], 0) + 1
          
        # Decrease the frequency 
        # of the first character 
        # of the previous substring 
        map[str[i - K]] -= 1
  
        # If the character is not present 
        # in the current substring 
        if (map[str[i - K]] == 0): 
            del map[str[i - K]] 
  
        # If the count of distinct 
        # characters is 0 
        if (len(map) == K): 
            answer += 1
  
    # Return the count 
    return answer 
  
# Driver code 
if __name__ == '__main__': 
      
    str = "aabcdabbcdc"
  
    # Integer K 
    K = 3
  
    # Print the count of K length 
    # substrings with k distinct characters 
    print(countSubstrings(str, K)) 
  
# This code is contributed by mohit kumar 29


C#
// C# program to find the count
// of k length substrings with k 
// distinct characters using 
// sliding window 
using System;
using System.Collections.Generic; 
  
class GFG{
  
// Function to return the 
// required count of substrings 
public static int countSubstrings(string str,
                                  int K) 
{ 
    int N = str.Length;
      
    // Store the count 
    int answer = 0; 
  
    // Store the count of 
    // distinct characters 
    // in every window 
    Dictionary map = new Dictionary(); 
  
    // Store the frequency of 
    // the first K length substring 
    for(int i = 0; i < K; i++) 
    { 
          
        // Increase frequency of 
        // i-th character
        if(!map.ContainsKey(str[i]))
        {
            map[str[i]] = 1;
        }
        else
        {
            map[str[i]]++; 
        }
    } 
  
    // If K distinct characters 
    // exist 
    if (map.Count == K) 
        answer++; 
  
    // Traverse the rest of the 
    // substring 
    for(int i = K; i < N; i++)
    { 
          
        // Increase the frequency 
        // of the last character 
        // of the current substring 
        if(!map.ContainsKey(str[i]))
        {
            map[str[i]] = 1;
        }
        else
        {
            map[str[i]]++; 
        }
          
        // Decrease the frequency 
        // of the first character 
        // of the previous substring
        map[str[i - K]]--;
  
        // If the character is not present 
        // in the current substring 
        if (map[str[i - K]] == 0)
        { 
            map.Remove(str[i - K]); 
        } 
  
        // If the count of distinct 
        // characters is 0 
        if (map.Count == K)
        { 
            answer++; 
        } 
    } 
  
    // Return the count 
    return answer; 
} 
  
// Driver code 
public static void Main(string[] args) 
{ 
      
    // string str 
    string str = "aabcdabbcdc"; 
  
    // integer K 
    int K = 3; 
  
    // Print the count of K length 
    // substrings with k distinct characters 
    Console.Write(countSubstrings(str, K));
} 
}
  
// This code is contributed by rutvik_56


输出:
5

时间复杂度: O(N)

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