[leetcode] 340. Longest Substring with At Most K Distinct Characters 解题报告

题目链接: https://leetcode.com/problems/longest-substring-with-at-most-k-distinct-characters/
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.

思路: 用一个队列+一个hash表, 每次将一个字符加到队列里去, 并且在hash表中将其计数+1, 如果hash表的长度大于k了, 说明现在字符超出了个数, 因此我们将队列的首元素出队列, 并且在hash表中将对应的字符计数-1, 如果这个字符的计数=0了, 那么就在hash表中删除这个字符, 直到hash表的长度<=k. 并且每次和队列长度比较更新最大长度.

代码如下:

class Solution {
public:
int lengthOfLongestSubstringKDistinct(string s, int k) {
if(s.size() == 0 || k <= 0) return 0;
unordered_map<char, int> mp;
queue<char> que;
int Max = 0;
for(int i = 0; i< s.size(); i++)
{
que.push(s[i]);
mp[s[i]]++;
while(mp.size() > k)
{
char ch = que.front();
que.pop();
mp[ch]--;
if(mp[ch] == 0)
mp.erase(ch);
}
Max = max(Max, (int)que.size());
}
return Max;
}
};