【C++】【LeetCode】3. Longest Substring Without Repeating Characters

link: Longest
Substring Without Repeating Characters

题目：

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.

注意点：

注意，如果使用两层从0到size的for循环，会导致时间复杂度过大，考虑将外层循环变量i跳值，从重复的字符的下一个开始取。

源码：

class Solution {
public:
int lengthOfLongestSubstring(string s) {
int max = 0;
int size = (int)s.size();
string newS = "";

for (int i=0; i<size-max; i++) { //如果i到最后一位的距离已经小于max，则没有必要继续
for (int j=i; j<size; j++) {
newS = s.substr(i, j-i+1);
int count = (int)newS.find(s[j+1]);
if (count >= 0) {
if (newS.size() > max) {
max = (int)newS.size();
}
i = i + count;
break;
}
newS = s.substr(i, j-i+2);
}
if (newS.size() > max) {
max = (int)newS.size();
}
}
return max;

}
};