3. Longest Substring Without Repeating Characters

Problem

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.

Solution (Java)

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.charAt(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;
    }
}

Solution (Javascript)

/**
 * @param {string} s
 * @return {number}
 */
var lengthOfLongestSubstring = function(s) {
  var map = {};
  var len = s.length;
  var max = 0;
  var start = 0;
  for (var i = 0; i < len; i++) {
    if (map[s[i]] !== undefined) {
      start = Math.max(start, map[s[i]] + 1);
    }
    map[s[i]] = i;
    max = Math.max(max, i - start + 1);
  }
  return max;
};

Explain:

nope.

Complexity:

• Time complexity : O(n).
• Space complexity : O(n).