找出字符串的最长不重复子串，输出长度和子串
方法一：穷举法，空间复杂度是O(1)，时间复杂度是O(N^4)
java代码实现
<pre name="code">public class Max_substring {public int max_unique_substring(char[] str){int maxlen = 0;int begin = 0;int n = str.length;for(int i = 0; i < n; ++i){for(int j = i+1; j < n; ++j){int flag = 0;//判断子串是否有重复字符for(int m = i; m < j; ++m){for(int k = m+1; k < j; ++k){if(str[m] == str[k]){flag = 1;break;}}if(1 == flag) break;}if(0 == flag && j-i+1 > maxlen){maxlen = j-i+1;begin = i;}}}StringBuffer s = new StringBuffer();for(int g = 0; g < n; &
