LeetCod-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.

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Analysis:

题意：

给定一个字符串，找到其中的一个最长的字串，使得这个子串不包含重复的字符。

方法：

利用双指针，开一个数组记录当前字符最近出现的位置，一遍算过去，更新左边界，用它计算最大值就行了。时间复杂度O(n),空间复杂度O(1).

Answer:

public class Solution {
public int lengthOfLongestSubstring(String s) {
int res=0,left=0;
int[] arr = new int[128];
for(int i=0;i<arr.length;i++){
arr[i]=-1;
}
for(int i=0;i<s.length();i++){
char temp = s.charAt(i);
if(arr[temp]>=left)
left = arr[temp]+1;
arr[temp]=i;
if(res< i-left+1)
res = i-left+1;
}
return res;
}
}