244. Shortest Word Distance II

    var map : [String:[Int]]
    init(_ words: [String]) {
        map = [String:[Int]]() // word , index array
        for (index, w) in words.enumerated() {
            map[w, default:[Int]()].append(index)
        }
    }

    func shortest(_ word1: String, _ word2: String) -> Int {
        let l1 = map[word1]!
        let l2 = map[word2]!
        var res = Int.max
        var p1 = 0
        var p2 = 0
        while p1 < l1.count && p2 < l2.count {
            res = min(res, abs(l1[p1] - l2[p2]))
            if l1[p1] < l2[p2] {
                p1 += 1
            }else{
                p2 += 1
            }
        }
        return res
    }