Untitled

class Solution {
    func lengthOfLongestSubstring(_ s: String) -> Int {
        var s = Array(s)
        var l = 0
        var ans = 0
        var d: [Character: Int] = [:]
        
        for r in 0..<s.count {
            if let oldL = d[s[r]] {
                l = max(l, oldL + 1)
            }
            
            d[s[r]] = r
            ans = max(ans, r - l + 1)
        }
        
        return ans
    }
}