LeetCode3-Longest Substring Without Repeating Characters(C++)

Description

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

Example 1:

Input: “abcabcbb”
Output: 3
Explanation: The answer is “abc”, with the length of 3.
Example 2:

Input: “bbbbb”
Output: 1
Explanation: The answer is “b”, with the length of 1.
Example 3:

Input: “pwwkew”
Output: 3
Explanation: The answer is “wke”, with the length of 3.
Note that the answer must be a substring, “pwke” is a subsequence and not a substring.

AC代码

class Solution {
public:
    int lengthOfLongestSubstring(std::string s) {
        // 计算机也是以整数的形式来存储char的，取值范围是0~255
        // 这个dict你也可以理解成一个字典，key是char的数值, value是它在s中的当前位置
        std::vector<int> dict(256, -1);
        // maxLen顾名思义，就是用来存储最终结果的
        // start就是用来存储子串的起始点的
        int maxLen = 0;
        int start = -1;
        for(int i=0; i<s.length(); i++) {
            // dict[s[i]] > start 代表这个char在之前已经出现过了
            // 这时需要更新起始点的位置
            if(dict[s[i]] > start) {
                start = dict[s[i]];
            }
            // 保存当前字符的位置
            dict[s[i]] = i;
            maxLen = std::max(maxLen, i - start);
        }
        return maxLen;
    }
};

测试代码

int main() {
    std::string a1 = "abcabcbb";
    std::string a2 = "bbbbb";
    std::string a3 = "pwwkew";

    Solution s;

    std::cout << s.lengthOfLongestSubstring(a1) << std::endl;
    std::cout << s.lengthOfLongestSubstring(a2) << std::endl;
    std::cout << s.lengthOfLongestSubstring(a3) << std::endl;
}

总结

上述的解法有一些巧妙。其实vector也可以换成map之类的数据结构。