【每天一道编程系列-2018.2.16】（Ans）

import java.util.Arrays;
import java.util.HashMap;
import java.util.Map;

/**
 * @author yesr
 * @create 2018-02-16 下午11:08
 * @desc
 **/
public class Test0216 {
    public int lengthOfLongestSubstring(String s) {
        if (s == null) {
            return 0;
        }

        int start = 0;
        int result = 0;
        Map<Character, Integer> map = new HashMap<>(s.length());

        for (int i = 0; i < s.length(); i++) {
            char ch = s.charAt(i);
            if (map.containsKey(ch) && map.get(ch) >= start) {
                start = map.get(ch) + 1;
            }
            else {
                result = Math.max(result, i - start + 1);
            }

            map.put(ch, i);
        }
        return result;
    }

    public int lengthOfLongestSubstring2(String s) {
        if (s == null) {
            return 0;
        }

        int[] appear = new int[256];
        Arrays.fill(appear, -1);
        int start = 0;
        int result = 0;

        for (int i = 0; i < s.length(); i++) {
            if (appear[s.charAt(i)] >= start) {
                start = i + 1;
            }
            else {
                result = Math.max(result, i - start + 1);
            }
            appear[s.charAt(i)] = i;
        }

        return result;
    }
}