3、无重复字符的最长子串

fun lengthOfLongestSubstring(s: String): Int {
    var maxLen = 0      // 最长不重复字串长度
    var startIndex = 0  // 当前子串起始索引
    var nowIndex = 0    // 当前子串的索引
    // 记录在当前子串中每个char的索引
    val charIndexMap = mutableMapOf<Char, Int>()
    // 查找最长非重复子串
    while (nowIndex < s.length) {
        val c = s[nowIndex]
        // 若子串中已存在该字符,并且字符索引在子串范围内
        if (charIndexMap.containsKey(c) && charIndexMap[c]!! >= startIndex) {
            startIndex = charIndexMap[c]!! + 1
            charIndexMap[c] = nowIndex++
        }else {// 否则加入或刷新map
            charIndexMap[c] = nowIndex++
            val len = nowIndex - startIndex
            maxLen = if (len > maxLen) len else maxLen
        }
    }
    return maxLen
}