leetcode 159: Longest Substring with At Most Two Distinct Characters，leetcodelongest

leetcode 159: Longest Substring with At Most Two Distinct Characters，leetcodelongest

Total Accepted: 1167 Total Submissions: 3961

Given a string, find the length of the longest substring T that contains at most 2 distinct characters.

For example,Given s = “eceba”,

T is "ece" which its length is 3.

[分析]

用HASHTABLE 記錄 當前兩個字元的數目, 如果遇到新字元, 移動start指標的位置, 直到新的start位置, 只包含兩個字元. 這題思路很簡單, 不知為何標為HARD. 也許有更優解, 不需要用extra space.

[code]

public class Solution {    public int lengthOfLongestSubstringTwoDistinct(String s) {        //input check        if(s== null || s.length()==0) return 0;        Map<Character, Integer> map = new HashMap<Character, Integer>();        int start = 0;        int max = 0;        for(int i=0; i<s.length(); i++) {            char c = s.charAt(i);            if(map.containsKey(c)) {                map.put( c,   map.get(c) + 1 );            } else if(map.size() < 2) {                map.put(c, 1);            } else {                while( (map.size()==2) && start<i) {                    char temp = s.charAt(start);                    int x = map.get(temp);                    --x;                    if(x==0) map.remove(s.charAt(start));                    else map.put(s.charAt(start), x);                    ++start;                }                map.put(c,1);            }            max = Math.max(max, i-start+1);        }        return max;    }}