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3. Longest Substring Without Repeating Characters

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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.

难度:medium

题目:
给定一字符串,找出最长且无重复字符的子串。

思路:

创建字符下标数组用以记录访问过的字符串中的字符。下标由1开始,用以区别数组的初始化值0.
定义子串的起始下标,子串的窗口为[begin indx, i]
Runtime: 19 ms, faster than 96.64% of Java online submissions for Longest Substring Without Repeating Characters.

class Solution {
public int lengthOfLongestSubstring(String s) {
if (null == s || “” == s) {
return 0;
}

int[] charIdxArray = new int[256];
int maxLen = 0;
int beginIdx = 0;
for (int i = 0; i < s.length(); i++) {
char c = s.charAt(i);
int idx = charIdxArray[c];
if (idx < 1 || idx <= beginIdx) {
charIdxArray[c] = i + 1;
} else {
beginIdx = idx;
charIdxArray[c] = i + 1;
}
maxLen = Math.max(maxLen, i + 1 – beginIdx);
}

return maxLen;
}
}

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