LeetCode(3)--Longest Substring Without Repeating Characters
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题目如下:
Given a string, find the length of the longest substring without repeating characters. For example, the longest substring without repeating letters for “abcabcbb” is “abc”, which the length is 3. For “bbbbb” the longest substring is “b”, with the length of 1.
解题思路:
找出数组中最长的字数组(无重复项)问题。
思路1:对数组遍历,遍历的同时将字数组存在map中,如果map中出现重复的字符ch时,将map中ch及其之前的删除,循环操作。如下图:
map里的变化:
结果是超时,改变一种思路。
思路2:利用一个exist数组保存字符是否出现(假设char set是ascii),从前向后遍历数组,如果遇到已存在的字符,应该回退到这个字符上次出现的下一个位置从新开始统计(如下图),同时注意exist数组的同步更新。
该方法来自:http://my.oschina.net/jdflyfly/blog/283405
提交代码:
public int lengthOfLongestSubstring(String s) { if (s == null || s.length() == 0) return 0; int res = 1; boolean[] exist = new boolean[256]; int start = 0; for (int i = 0; i < s.length(); i++) { char ch = s.charAt(i); if (exist[ch]) { res = Math.max(res, i - start); for (int k = start; k < i; k++) { if (s.charAt(k) == ch) { start = k + 1; break; } exist[s.charAt(k)] = false; } } else exist[ch] = true; } res = Math.max(res, s.length() - start); return res; }
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