[leetcode] Longest Substring Without Repeating Characters

 

O(N^2)AC..

class Solution {

public:
    int lengthOfLongestSubstring(string s) {
        int n = s.length();
        if( n == 0 )
            return 0;
        int ans = 0, i, j;
        int start = 0;
        for(i=0; i<n; i++) {
            for(j=i-1; j>=start; j--) {
                if(s[j] == s[i]) {
                    start = j+1;
                    break;
                }
            }
            ans = max(ans, i-j);
        }
        return ans;
    }
};

 使用hash表优化查询...

class Solution {

public:
    int lengthOfLongestSubstring(string s) {
        int n = s.length();
        int ans = 0, i, j;
        int start = 0;
        bool vis[128] = {false};
        for(i=0; i<n; i++) {
            if(!vis[s[i]]) {
                vis[s[i]] = true;
            } else {
                while(s[start] != s[i]) {
                    vis[s[start]] = false;
                    start++;
                }
                start++;
            }
            ans = max(ans, i-start+1);
        }
        return ans;
    }
};