leetcode 3. 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 asubstring,

"pwke"

is a subsequence and not a substring.

思路

L[i]表示当前最长不重复子串s[m..i]，然后讨论L[i+1],显然有两种情况，当s[i+1],未出现过时，L[i+1]=s[m..i+1]；当s[i+1] 出现过时,下标为K，更新m=max(k+1,m);

最大长度=max（logest,i-m+1），可以用ascii码将字符存在数组里

代码

int lengthOfLongestSubstring(string s) {
// for ASCII char sequence, use this as a hashmap
vector<int> charIndex(256, -1);
int longest = 0, m = 0;

for (int i = 0; i < s.length(); i++) {
m = max(charIndex[s[i]] + 1, m);
       charIndex[s[i]] = i;
longest = max(longest, i - m + 1);
}

return longest;
}