LeetCode 340. Longest Substring with At Most K Distinct Characters

最新推荐文章于 2023-04-14 19:10:16 发布

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本文介绍了一种算法，该算法通过两种方法找到给定字符串中最长的包含最多K种不同字符的子串。这两种方法分别是使用队列和哈希表的方法，以及双指针技巧。文章提供了完整的代码实现，并通过示例进行说明。

#include <iostream>
#include <queue>
#include <unordered_map>
#include <vector>
using namespace std;

/*
  Given a string, find the length of the longest substring T that contains at
  most K distinct characters.
  For example:
  Given s = "eceba" and k = 2, T is "ece" which its length is 3.
*/

// using a queue to push the characters. 
int longestSubstringWithKDistinct(string s, int k) {
  if(s.size() <= k) return s.size();
  int i = 0;
  int maxSize = 0;
  queue<char> chars;
  unordered_map<char, int> hashMap;
  while(i < s.size()) {
    chars.push(s[i]);
    hashMap[s[i]]++;
    while(hashMap.size() > k) {
      char ch = chars.front();
      chars.pop();
      hashMap[ch]--;
      if(hashMap[ch] == 0) hashMap.erase(ch);
    }
    maxSize = max(maxSize, (int)chars.size());
    i++;
  }
  return maxSize;
}

// two pointers.
int longestSubStringK(string s, int k) {
  if(s.size() <= k) return s.size();
  vector<int> hashMap(256, 0);
  int maxSize = 0;
  int count = 0;
  int i = 0;
  int j = 0;
  while(i < s.size()) {
    if(hashMap[s[i]] == 0) {
        hashMap[s[i]]++;
        count++;
    } else {hashMap[s[i]]++;}
    if(count > k) {
      maxSize = max(maxSize, i - j);
      while(--hashMap[s[j++]] > 0) {
      }
      count--;
    }
    i++;
  }
  maxSize = max(maxSize, i - j);
  return maxSize;
}

int main(void) {
  cout << longestSubstringWithKDistinct("ecebaddde", 2) << endl;
  cout << longestSubStringK("ecebaddde", 2) << endl;
}