[LeetCode160]Longest Substring with At Most Two Distinct Characters

SharonMoMo

于 2015-11-24 05:19:48 发布

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分类专栏： LeetCode 文章标签： leetcode

本文链接：https://blog.youkuaiyun.com/u012175043/article/details/50007351

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本文介绍了一种使用哈希表和双指针技术解决寻找字符串中最长包含最多两个不同字符的子串问题的方法。通过更新起始点实现高效查找。

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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.

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Hide Similar Problems (M) Longest Substring Without Repeating Characters (H) Sliding Window Maximum

记得看到一个blog说：这种题，一般都在于用一个hash table 和两个reference。不同之处在于如何update start point.

class Solution {
public:
    int lengthOfLongestSubstringTwoDistinct(string s) {
        if(s.empty()) return 0;
        int dict[256] = {0};
        int cnt = 0, start = 0, maxLen = 1;
        for (int i = 0; i<s.size(); ++i) {
            ++dict[s[i]];
            if (dict[s[i]] == 1) { // new char
                ++cnt;
                while (cnt > 2) {
                    --dict[s[start]];
                    if(!dict[s[start]]) --cnt; // mp[s[i] indicates: from start to current position, how many s[i] the substr has. if(!mp[s[start]]) then s[start] no longer exist we can --cnt;
                    ++start;
                }
            }
            maxLen = max(maxLen, i-start + 1);
        }
        return maxLen;
    }
};