dev/leetcode/longestsubstring

Longest Substring Without Repeating Characters

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

Example 1:

Input: “abcabcbb”
Output: 3
Explanation: The answer is “abc”, with the length of 3.

Example 2:

Input: “bbbbb”
Output: 1
Explanation: The answer is “b”, with the length of 1.

Example 3:

Input: “pwwkew”
Output: 3
Explanation: 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.

Solution 1

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private static int lengthOfLongestSubstring(String s) {
Set<Character> substring = new HashSet<>();
int res = 0;

if (s == null) {
return res;
}

for (int i = 0; i < s.length(); i++) {
int temp = 0;
int j = i;
while (j < s.length()) {
if (!substring.contains(s.charAt(j))) {
substring.add(s.charAt(j++));
temp++;
} else {
substring.clear();
break;
}
}
res = Math.max(temp, res);
}

return res;

/**
执行用时 :127 ms, 在所有 Java 提交中击败了10.50%的用户
内存消耗 :42.3 MB, 在所有 Java 提交中击败了5.02%的用户
*/
}

Using too much time, so I read the leetcode document.
Here is a SlideWindow method.

Solution 2

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private static int plus(String s) {
int res = 0;
Set<Character> set = new HashSet<>();
int i = 0, j = i;

while (j < s.length()) {
if (!set.contains(s.charAt(j))) {
set.add(s.charAt(j++));
res = Math.max(res, set.size());
} else {
set.remove(s.charAt(i++));
}
}

return res;

/**
执行用时 :10 ms, 在所有 Java 提交中击败了64.95%的用户
内存消耗 :41.6 MB, 在所有 Java 提交中击败了5.02%的用户
*/

We can adjust the SlideWindow by increase i - head pointer and j - rear pointer.
This can sharply optimize the complexity of time.

Reference
https://leetcode-cn.com/problems/longest-substring-without-repeating-characters