leetcode-3:Longest Substring Without Repeating Characters

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

Example 1:

Input: "abcabcbb"
Output: 3
Explanation: The answer is "abc", which the length is 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.

Solution1 26ms

建一个map<char,int>滑动窗口，对每一个end位置，调整start位置，使得map中的数值小于等于1

class Solution {
public:
    int lengthOfLongestSubstring(string s) {
        map<char,int> cmap;
        int start = 0;
        int length;
        int length_max=0;
        for (int i =0;i<s.length();i++)
        {
            char c = s[i];
            if(cmap.find(c)!=cmap.end()){cmap[c]++;}
            else{cmap[c]=1;}
            while(cmap[c]>1){
                char ctmp = s[start];
                cmap[ctmp] --;
                start++;
            }
            length = i-start+1;
            length_max = length>length_max?length:length_max;
        }
        return length_max;
    }
};

Solution2 16ms

建一个256维的int数组，数组中的int * idx（0-256）代表char类型的256种字符，idx处存储的int 值表示自end往前，上一次遇到该字符的位置，如果在idx处再遇到同样的字符，那就把窗口的start设为该字符上一次遇到的位置

class Solution {
public:
    int lengthOfLongestSubstring(string s) {
        vector<int> map(256,-1);
        int start = -1;
        int maxlength =0;
        for(int i = 0;i<s.length();i++){
            if(map[s[i]]>start){
                start = map[s[i]];
            }
            map[s[i]]=i;
            maxlength = max(maxlength,i-start);
        }
        return maxlength;
    }
};

Note

加上下面一段代码，solution1 速度可以提升到16ms，solution2速度可以提升到8ms

static const auto io_sync_off = []() {
    std::ios::sync_with_stdio(false);
    std::cin.tie(nullptr);
    return nullptr;
}();

网上的解释：

一般情况下不用函数库优化的话，大数据输入输出c语言比c++快一倍多，运行效率也会高一些这是c语言更接近低端语言，容易识别你应该是初学吧，很多地方要用函数优化c++才会体现它的优越性比如cin在#include <algorithm>头文件下主函数中+入 std::ios::sync_with_stdio(false) 会大幅提高效率，最后会比scanf还快0.5倍 cin慢在它输入时与stdin同步，尤其是在文件输入输出时特别慢但关闭同步功能后马上速度就快了

leetcode-3:Longest Substring Without Repeating Characters

Note

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