lintcode:Longest Substring Without Repeating Characters

原创于 2015-05-17 17:55:58 发布 · 355 阅读

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本文介绍了一种求解字符串中最长无重复字符子串长度的高效算法，并提供了C++实现示例。通过动态规划方法及哈希表记录字符位置，确保了O(n)的时间复杂度。

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Given a string, find the length of the longest substring without repeating characters.

Example

For example, the longest substring without repeating letters for"abcabcbb" is "abc", which the length is 3.

For "bbbbb" the longest substring is "b", with the length of 1.

Challenge

O(n) time

class Solution {
public:
    /**
     * @param s: a string
     * @return: an integer 
     */
    int lengthOfLongestSubstring(string s) {
        // write your code here
        vector<int> dp(s.size()+1);
        map<int, int> posMap;
        
        dp[0] = 0;
        int retMax = 0;
        
        for (int i=0; i<s.size(); i++)
        {
            if (posMap.count(s.at(i)) == 0)
            {
                dp[i+1] = dp[i]+1;
            }
            else
            {
                dp[i+1] = min(i-posMap[s.at(i)], dp[i]+1);
            }
            
            posMap[s.at(i)] = i;
            
            retMax = max(retMax, dp[i+1]);
        }
        
        return retMax;
    }
};