LeetCode-in-All

3. Longest Substring Without Repeating Characters

Medium

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

Example 1:

Input: s = “abcabcbb”

Output: 3

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

Example 2:

Input: s = “bbbbb”

Output: 1

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

Example 3:

Input: s = “pwwkew”

Output: 3

Explanation: The answer is “wke”, with the length of 3. Notice that the answer must be a substring, “pwke” is a subsequence and not a substring.

Example 4:

Input: s = “”

Output: 0

Constraints:

Solution

public class Solution {
    public int LengthOfLongestSubstring(string s) {
        int[] lastIndices = new int[256];
        for (int i = 0; i < 256; i++) {
            lastIndices[i] = -1;
        }
        int maxLen = 0;
        int curLen = 0;
        int start = 0;
        for (int i = 0; i < s.Length; i++) {
            char cur = s[i];
            if (lastIndices[cur] < start) {
                lastIndices[cur] = i;
                curLen++;
            } else {
                int lastIndex = lastIndices[cur];
                start = lastIndex + 1;
                curLen = i - start + 1;
                lastIndices[cur] = i;
            }
            if (curLen > maxLen) {
                maxLen = curLen;
            }
        }
        return maxLen;
    }
}