Leetcode题解-3. 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：用一个大小为128的int数组，0代表这个符号没有出现，1代表出现了，从字符串头开始读起，把每个字符用对应的ascall码装填到数组里，当发现当前字符已经存在，寻找该字符在该字符串第一次出现的位置，把字符串头到该位置之间的子串删除，从该位置的下一位重新开始读，直到字符串的结尾。

    该思路的时间复杂度是O（n^2），需要128*sizeof(int)的空间

int lengthOfLongestSubstring(string s) {
     int appear[127] = {0};
     int flag = 0;
     int max = 0, current = 0;
     while(flag != s.size()){
     	if(appear[s[flag] ] == 1){
     		if(max < current) max = current;
     		current = 0;
     		memset(appear, 0, 127*sizeof(int));
            int cut = s.find(s[flag]);
     		s.erase(0, cut+1);
     		flag = 0;
     	}
     	else{
     		appear[s[flag]] = 1;
     		current ++;
     		flag++;
     	}
     }
        if(max < current) max = current;
     return max;
    }