沒有重複字元的最長子串

問題

暴力方法將涉及創建給定字串的所有可能的子字串，並找出哪個是最長的沒有重複字元的子字串。這將導致 TC:O(n^2)

最佳方法：
TC：O(n)
SC : O(256)，用於使用大小為 256 的 int[]

class Solution {
    public int lengthOfLongestSubstring(String s) {
        int hash[] = new int[256];// size of all the ascii characters
        Arrays.fill(hash,-1); // -1 to indicate these indexes don't have any character visited already
        int left =0,right =0;
        int max = 0;
        while(right<s.length()){
            char  c = s.charAt(right);
            if(hash[c]!=-1){// means the character has been seen in the past
                if(hash[c]>=left){// if the index of the character seen in the past is after the left pointer, then left pointer should be updated, to avoid duplicate in the window of substring
                    left  = hash[c] + 1;// has to be 1 index after the index of last seen duplicate character
                }
            }
            max = Integer.max(max, right-left+1);// keep track of mas window substring
            hash[c]  = right;// update the character last seen index in hash
            right++;
        }
        return max;
    }
}

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