Given a string, find the length of the longest substring without repeating characters. For example, the longest substring without repeating letters for "abcabcbb" is "abc", which the length is 3. For "bbbbb" the longest substring is "b", with the length of 1.

LeetCode-Longest Substring Without Repeating Characters

C++:
class Solution {
private:
    bool canUse[256];
public:
    int lengthOfLongestSubstring(string s) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        memset(canUse,true,sizeof(canUse));
        int start=0;
        int count=0;
        int ret=0;
        for(int i=0;i<s.size();i++){
            if(canUse[s[i]]==true){
                canUse[s[i]]=false;
                count++;
            }else{
                ret=max(ret,count);
                while(true){
                    canUse[s[start]]=true;
                    count--;
                    if(s[start]==s[i]) break;
                    start++;
                }
                start++;
                canUse[s[i]]=false;
                count++;
            }
        }
        ret=max(ret,count);
        return ret;
    }
};
Java:
public class Solution {
    private boolean[] canUse=new boolean[256];
    public int lengthOfLongestSubstring(String s) {
        // Start typing your Java solution below
        // DO NOT write main() function
        Arrays.fill(canUse,true);
        int start=0;
        int count=0;
        int ret=0;
        for(int i=0;i<s.length();i++){
            if(canUse[s.charAt(i)]){
                canUse[s.charAt(i)]=false;
                count++;
            }else{
                ret=Math.max(ret,count);
                while(true){
                    canUse[s.charAt(start)]=true;
                    count--;
                    if(s.charAt(start)==s.charAt(i)) break;
                    start++;
                }
                start++;
                canUse[s.charAt(i)]=false;
                count++;
            }
        }
        ret=Math.max(ret,count);
        return ret;
    }
}