[Swift]LeetCode1081. 不同字符的最小子序列 | Smallest Subsequence of Distinct Characters

★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★
➤微信公众号：山青咏芝（shanqingyongzhi）
➤博客园地址：山青咏芝（https://www.cnblogs.com/strengthen/）
➤GitHub地址：https://github.com/strengthen/LeetCode
➤原文地址：https://www.cnblogs.com/strengthen/p/10993157.html  
➤如果链接不是山青咏芝的博客园地址，则可能是爬取作者的文章。
➤原文已修改更新！强烈建议点击原文地址阅读！支持作者！支持原创！
★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★

热烈欢迎，请直接点击！！！

进入博主App Store主页，下载使用各个作品！！！

注：博主将坚持每月上线一个新app！！！

Return the lexicographically smallest subsequence of text that contains all the distinct characters of textexactly once. 

Example 1:

Input: "cdadabcc"
Output: "adbc"

Example 2:

Input: "abcd"
Output: "abcd"

Example 3:

Input: "ecbacba"
Output: "eacb"

Example 4:

Input: "leetcode"
Output: "letcod" 

Note:

1. 1 <= text.length <= 1000
2. text consists of lowercase English letters.

---

返回字符串 text 中按字典序排列最小的子序列，该子序列包含 text 中所有不同字符一次。 

示例 1：

输入："cdadabcc"
输出："adbc"

示例 2：

输入："abcd"
输出："abcd"

示例 3：

输入："ecbacba"
输出："eacb"

示例 4：

输入："leetcode"
输出："letcod" 

提示：

1. 1 <= text.length <= 1000
2. text 由小写英文字母组成

---

12ms

class Solution {

    func smallestSubsequence(_ text: String) -> String {
        var cnt = [Int](repeating: 0, count: 26) , used = cnt
        var idx = 0, dic = [Character: Int](), chars = Array(text)
        _ = "abcdefghijklmnopqrstuvwxyz".map { dic[$0] = idx; idx += 1 }
        for ch in chars {
            let idx = dic[ch]!
            let ct = cnt[idx]
            cnt[idx] = ct + 1
        }

        var ans = ""
        for ch in chars {
            let idx = dic[ch]!
            let ct = cnt[idx]
            cnt[idx] = ct - 1

            let uct = used[idx]
            used[idx] = uct + 1
            if uct > 0 { continue }
            while !ans.isEmpty && ans.last! > ch && cnt[dic[ans.last!]!] > 0 {
                used[dic[ans.last!]!] = 0
                ans.removeLast()
            }
            ans += "\(ch)"
        }
        return ans
    }
}

---

Runtime: 16 ms

Memory Usage: 21.4 MB

class Solution {
    func smallestSubsequence(_ text: String) -> String {
        var cnt:[Int] = [Int](repeating:0,count:26)
        var used:[Int] = [Int](repeating:0,count:26)
        var res:[Character] = [Character]()
        let arrText:[Character] = Array(text)
        let arrIndex:[Int] = Array(text).map{$0.ascii - 97}
        for i in arrIndex
        {
            cnt[i] += 1
        }
        for (index,i) in arrIndex.enumerated()
        {
            cnt[i] -= 1
            if used[i]++ > 0 {continue}
            while(!res.isEmpty && (res.last!.ascii - 97) > i && cnt[res.last!.ascii - 97] > 0)
            {
                used[res.last!.ascii - 97] = 0
                res.popLast()
            }
            res.append(arrText[index])
        }
        return String(res)
    }
}

//Character扩展
extension Character
{
    //Character转ASCII整数值(定义小写为整数值)
    var ascii: Int {
        get {
            return Int(self.unicodeScalars.first?.value ?? 0)
        }
    }
}

/*扩展Int类，实现自增++、自减--运算符*/
extension Int{
    //后缀++:先执行表达式后再自增
    static postfix func ++(num:inout Int) -> Int {
        //输入输出参数num
        let temp = num
        //num加1
        num += 1
        //返回加1前的数值
        return temp
    }
}