LeetCode:3. 无重复字符的最长子串

/**
 * @param {string} s
 * @return {number}
 */
var lengthOfLongestSubstring = function(s) {
    let start = 0,end = 0;
    let mp = new Map();
    let ans = 0;
    while(end<s.length)
    {
        
        let pos = mp.get(s[end]);
        if(mp.has(s[end])&&pos>=start)
        {
            start = mp.get(s[end])+1;
        }
        mp.set(s[end],end);
        ans = Math.max(ans,end-start+1);
        end++;
    }
    return ans;
};