Leetcode-159.Longest Substring with At Most Two Distinct Characters

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最新推荐文章于 2025-05-29 11:07:30 发布

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本文介绍了一种求解字符串中最长包含至多两种不同字符的子串算法。通过使用unordered_set来跟踪当前子串中的独特字符，并在遇到第三个新字符时调整窗口，确保子串始终符合题目要求。

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Problem Description:
Given a string, find the length of the longest substring T that contains at most 2 distinct characters.

For example, Given s = “eceba”,
T is “ece” which its length is 3.

Analysis:
We use a unordered_set to store the distinct characters,
if the size of st is less than 2 or its size is equal to 2,
but the current char is in the st, we insert the char to st. len increment by 1
when the size of st is 2, and meet another char, we need clear the st, and insert the current char. Also we need to reinsert the previous char as much as possible(keep the st has 2 chars).then we can move forward.
For example :
ceccbbbbb
the result should be : ccbbbbb.

codes:

int lengthOfLongestSubstringTwoDistinct(string s) {
    unordered_set<char> st;
    int n = s.size();
    int maxlen = 0, len = 0;
    for (int i = 0; i < n; ++i)
    {
        if (st.size() < 2 || st.size() == 2 && st.count(s[i]) > 0)
        {
        st.insert(st);
        len++
        }
        else {
            maxlen = max(maxlen, len);
            st.clear();
            int pos = i;
            st.insert(s[i--]);
            len = 1;
            while (i && (st.size() < 2 || (st.size() == 2 && st.count(s[i]) > 0)))
            {
                st.insert(s[i--]);
                len++;
            }
            i = pos + 1;
        }
        return max(maxlen, len);
    }

}