leetcode－－3

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1. 题目：

Longest Substring Without Repeating Characters

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

2. c++

2.1

class Solution {
public:
    int lengthOfLongestSubstring(string s) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        /*void *memset(void *s, int ch, unsigned n); 
将s所指向的某一块内存中的每个字节的内容全部设置为ch指定的ASCII值, 块的大小由第三个参数指定,这个函数通常为新申请的内存做初始化工作, 其返回值为指向S的指针。
需要的头文件<memory.h> or <string.h>  */

　　　　　int locs[256];            //保存字符上一次出现的位置
        memset(locs, -1, sizeof(locs)); 
        int idx = -1, max = 0;    //idx为当前子串的开始位置-1
        for (int i = 0; i < s.size(); i++)
        {
            if (locs[s[i]] > idx)//如果当前字符出现过，那么当前子串的起始位置为这个字符上一次出现的位置+1
            {
                idx = locs[s[i]];
            }

            if (i - idx > max)
            {
                max = i - idx;
            }

            locs[s[i]] = i;
        }
        return max;
    }
};

2.2

class Solution { 
public: 
      int lengthOfLongestSubstring(string s) {   
      int n = s.length();   
      int i = 0, j = 0;   
      int maxLen = 0;   
      bool exist[256] = { false };   
      while (j < n) {   
        if (exist[s[j]]) {   
          maxLen = max(maxLen, j-i);   
          while (s[i] != s[j]) {   
            exist[s[i]] = false;   
            i++;   
          }   
          i++;   
          j++;   
        } else {   
          exist[s[j]] = true;   
          j++;   
        }   
      }   
      maxLen = max(maxLen, n-i);   
      return maxLen;   
    }   
};

leetcode－－3

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原文地址：http://www.cnblogs.com/zxqstrong/p/4561902.html