LeetCode：3.Longest Substring Without Repeating Characters

思路：看到题目首先想到最大字符串匹配KMP算法

public static int lengthOfLongestSubstring(String s) {
        int maxLength = 0;
        StringBuilder sb = new StringBuilder(s);
        a:for(int i = 0;i<sb.length();i++){
            StringBuilder sb2 = new StringBuilder("");
            sb2.append(sb.substring(i,i+1));
            b:for(int j=i+1;j<sb.length();j++){
                c:for(int k =0;k<sb2.length();k++){
                    if(!sb.substring(j,j+1).equals(sb2.substring(k,k+1))){

                    }else{
                        if(maxLength<j-i)
                            maxLength = j-i;
                        break b;
                    }
                    if(k == sb2.length())
                        sb2.append(sb.substring(j,j+1));
                }
            }
        }
        return maxLength;
}

参考后代码

public static int lengthOfLongestSubstring(String s) {
        int n = s.length(), ans = 0;
        Map<Character, Integer> map = new HashMap<>(); // current index of character
        // try to extend the range [i, j]
        for (int j = 0, i = 0; j < n; j++) {
            if (map.containsKey(s.charAt(j))){
                i = Math.max(map.get(s.charAt(j)), i);
            }
            ans = Math.max(ans, j - i + 1);
            map.put(s.charAt(j), j + 1);
        }
        return ans;
    }