【原創】3. Longest Substring Without Repeating Characters --- leetcode算法筆記

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.

思路：兩個指針:begin和end。begin指向無重複字符的子串的頭，end指向無重複支付的子串的尾。

一個整型數組:charIndices，長度爲128（ascii字符有128個），每一位保存對應字符出現在s中的位置。

從頭遍歷s，若charIndices中當前字符對應的值大於begin，表示子串中出現了重複字符。此時，判斷子串長度，並將begin指向重複字符的下一位。最後將當前字符的位置保存在整型數組中。

遍歷完成後不要忘記再判斷子串長度。

Java代碼：

 

public int lengthOfLongestSubstring(String s) {
        if(s.equals("")) return 0 ;
        int[] charIndices = new int[128] ;
        for(int i = 0 ;i < charIndices.length ;i ++) charIndices[i] = -1 ;
        int begin = 0 ;
        int end = 0 ;
        int index = -1;
        int length = 0 ; 
        for(int i = 0;i < s.length() ; i++){
            end = i ;
            index = (int)s.charAt(i) ;
            if(charIndices[index] >= begin){
                if(end - begin > length){
                    length = end - begin ;  
                }
                begin = charIndices[index] + 1 ;
            }
            charIndices[index] = i ;
        }
        if(end + 1 - begin > length){
            length = end + 1 - begin ;  
        }
        return length ;
    }