leetcode p3 Longest Substring Without Repeating Characters

3. Longest Substring Without Repeating Characters

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

Examples:

Given "abcabcbb", the answer is "abc", which the length is 3.

Given "bbbbb", the answer is "b", with the length of 1.

Given "pwwkew", 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.

思路:

因为只是一个字符串,只涉及到ascii码 ,所以我们将所有的出现的字符序号维持在一个256的数组next(即a在字符串中的序号为1, 

那么next[97] = 1,但是序号为2的也是a,那么就会更新next[97] = 2)中,再维持一个变量start(默认为-1)表示最近出现重复字符的序号(比如aba,

当扫描到第一个a的时候,此时没有重复的,那么start=-1, 然后到b也是没有重复,之后到第二个a,那么此时就更新start为之前a的序号即start=0)

代码(python):

class Solution(object):
    def lengthOfLongestSubstring(self, s):
        """
        :type s: str
        :rtype: int
        """
        leng = len(s)
        next = [-1]*(256)
        start=-1
        max_len = 0
        for i in xrange(leng):
            if next[ord(s[i])] > start:
                start = next[ord(s[i])]
            next[ord(s[i])] = i
            max_len = max(max_len, i-start)
        return max_len

while True:
    print Solution().lengthOfLongestSubstring(raw_input())

c++

#include<iostream>
#include<string>
#include<vector>
#include<cmath>

using namespace std;

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

int main(){
    Solution a = Solution();
    string temp;
    cin>>temp;
    cout<<(a.lengthOfLongestSubstring(temp));
    return