3. Longest Substring Without Repeating Characters

经典问题，最长连续子串，DP解决

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.

package l3;

/*
 * DP考虑的是到当前就没有数据的情况
 * 后面的结果依赖于前面的结果
 */
public class Solution {
    public int lengthOfLongestSubstring(String s) {
    	if(s.equals(""))	return 0;
        char[] cs = s.toCharArray();
        int start = 0, end = 0;
        int []nearest_pos = new int[256];
        boolean []exist = new boolean[256];
        
        int max = 1;
        for(int i=0; i<cs.length; i++) {
        	if(! exist[cs[i]]) {
        		end = i;
        		exist[cs[i]] = true;
        		nearest_pos[cs[i]] = i;
        		if(end - start + 1 > max) max = end - start + 1;
        	} else {
        		for(int j=start; j<nearest_pos[cs[i]]; j++)	exist[cs[j]] = false;
        		start = nearest_pos[cs[i]] + 1;
        		nearest_pos[cs[i]] = i;
        		end = i;
        	}
        }
        
    	return max;
    }
}